Boltzmann Concept

54
Boltzmann’s Concepts of Reaction Rates Boltzmann’s Concepts of Reaction Rates V e l o c C o l l i s i M e a n V i s c o D e r i v E n e r M a x w e l l - B B a r o m e t r B o l t z m a n 02/27/12

Transcript of Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction Rates

Boltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i

M e a n

V i s c o

D e r i v

E n e r

M a x w e l l - B

B a r o m e t r

B o l t z m a n

022712

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0 5000 1 104

15 104

2 104

25 104

0

24 104

48 104

72 104

96 104

12 105

P2 h1( )

Pa

P3 h1( )

Pa

P h1( )

Pa

h1

m

Distribution of Air Particles

Distribution of Air Particles

Num

ber

Height

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PS 5

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Distribution of Molecular Energy Levels

Distribution of Molecular Energy Levels

Equation Boltzmanne g

g

N

N kT E

j

i

j

i ∆minus

sdot=

Where ∆ E = Ei ndash E j amp e-∆ EkT = Boltzman Factor

If Boltz Factor Comment

∆ E ltlt kT Close to 1 Ratio of population is equal

∆ E ~ kT 1e = 0368 Upper level drops suddenly

∆ E gtgt kT About 0 Zero upper level population

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The Barometric Formulation

The Barometric Formulation

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

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MB Distribution NormalizationMB Distribution Normalization

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

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Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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0 5000 1 104

15 104

2 104

25 104

0

24 104

48 104

72 104

96 104

12 105

P2 h1( )

Pa

P3 h1( )

Pa

P h1( )

Pa

h1

m

Distribution of Air Particles

Distribution of Air Particles

Num

ber

Height

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PS 5

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Distribution of Molecular Energy Levels

Distribution of Molecular Energy Levels

Equation Boltzmanne g

g

N

N kT E

j

i

j

i ∆minus

sdot=

Where ∆ E = Ei ndash E j amp e-∆ EkT = Boltzman Factor

If Boltz Factor Comment

∆ E ltlt kT Close to 1 Ratio of population is equal

∆ E ~ kT 1e = 0368 Upper level drops suddenly

∆ E gtgt kT About 0 Zero upper level population

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The Barometric Formulation

The Barometric Formulation

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

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httpslidepdfcomreaderfullboltzmann-concept 1654

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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httpslidepdfcomreaderfullboltzmann-concept 1854

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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PS 5

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Distribution of Molecular Energy Levels

Distribution of Molecular Energy Levels

Equation Boltzmanne g

g

N

N kT E

j

i

j

i ∆minus

sdot=

Where ∆ E = Ei ndash E j amp e-∆ EkT = Boltzman Factor

If Boltz Factor Comment

∆ E ltlt kT Close to 1 Ratio of population is equal

∆ E ~ kT 1e = 0368 Upper level drops suddenly

∆ E gtgt kT About 0 Zero upper level population

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The Barometric Formulation

The Barometric Formulation

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

822019 Boltzmann Concept

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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httpslidepdfcomreaderfullboltzmann-concept 2054

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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Distribution of Molecular Energy Levels

Distribution of Molecular Energy Levels

Equation Boltzmanne g

g

N

N kT E

j

i

j

i ∆minus

sdot=

Where ∆ E = Ei ndash E j amp e-∆ EkT = Boltzman Factor

If Boltz Factor Comment

∆ E ltlt kT Close to 1 Ratio of population is equal

∆ E ~ kT 1e = 0368 Upper level drops suddenly

∆ E gtgt kT About 0 Zero upper level population

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The Barometric Formulation

The Barometric Formulation

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

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MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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The Barometric Formulation

The Barometric Formulation

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

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MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

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httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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The Barometric Formulation

The Barometric Formulation

bull Calculate the pressure at mile high city (Denver CO) [1 mile= 1610 m] Po = 101325 kPa T = 300 K Assume 200 and800 mole of oxygen gas and nitrogen gas respectively

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Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

822019 Boltzmann Concept

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

822019 Boltzmann Concept

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

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MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

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Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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httpslidepdfcomreaderfullboltzmann-concept 754

Molecular TemperatureMolecular Temperature

Distribution Measurement of

Vibrational Temp in Hot GasesPlasmas Explosions

Rotational Low Temp in Interstellar Gases

Electronic High Stellar Temp of Atoms and Ions

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

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httpslidepdfcomreaderfullboltzmann-concept 954

K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

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httpslidepdfcomreaderfullboltzmann-concept 1154

1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

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httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

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httpslidepdfcomreaderfullboltzmann-concept 1354

1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

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httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

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httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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The Kinetic Molecular Model for

Gases ( Postulates )The Kinetic Molecular Model for

Gases ( Postulates )

bull Gas consists of large number of smallindividual particles with negligible size

bull Particles in constant random motion andcollisions

bull No forces exerted among each other

bull Kinetic energy directly proportional totemperature in Kelvin

T R KE sdotsdot=

2

3

822019 Boltzmann Concept

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

822019 Boltzmann Concept

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

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httpslidepdfcomreaderfullboltzmann-concept 1354

1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

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httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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K-M Model Root-Mean-Square SpeedK-M Model Root-Mean-Square Speed

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

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MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2154

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2454

Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Maxwell-Boltzmann DistributionMaxwell-Boltzmann Distribution

M-B Equation gives distribution of molecules in terms of

bullSpeedVelocity and

bullEnergy

One-dimensional Velocity Distribution in the x-direction

[ 1Du-x ]

x

T k um

due A N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1354

1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2154

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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1500 1000 500 0 500 1000 15000

5 104

0001

00015

0002

00025

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m 1minus ssdot

15001500minus u

m s1minussdot

x

T k um

due A

N

dN x

sdotsdot=sdotsdotsdotminus

2

1 2

Mcad

822019 Boltzmann Concept

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MB Distribution NormalizationMB Distribution Normalization

822019 Boltzmann Concept

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1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

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Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1254

MB Distribution NormalizationMB Distribution Normalization

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httpslidepdfcomreaderfullboltzmann-concept 1354

1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1354

1D-x Maxwell-Boltzmann Distribution1D-x Maxwell-Boltzmann Distribution

One-dimensional Velocity Distribution in the x-direction [ 1Du-x ]

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdot

sdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

One-dimensional Energy Distribution in the x-direction [ 1DE-x ]

xT k

x

E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3154

Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1454

x

T k um

u D

dueT k

m

N

dN x

x

sdotsdotsdotsdotsdot

=

sdotsdotsdotminus

minus

2

1

1

2

2 π

x

T k

x E D

d eT k N

dN x

x

ε ε

π

ε sdotsdotsdotsdotsdotsdot

=

sdotminusminus

minus

2

1

1 4

1

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2054

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2154

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2454

Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2654

Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2854

Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3154

Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1554

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

3D Velocity Distribution [ 3Du ] Let a = m2kT

xau

u D

duea

N

dN x

x

sdotsdot=

minus

minus

2

1 π

Cartesian Coordinates

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

y

au

u D due

a

N

dN y

y sdotsdot=

minus

minus

2

1 π z

au

u D due

a

N

dN z

z sdotsdot=

minus

minus

2

1 π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1654

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1854

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Re-shape box into sphere of same volume with radius u

V = (43) π u3 with u2 = ux2 + uy

2 + uz2

dV = dux duy duz = 4 π u2 du

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

z y x

uuua

D

dududuea

N

dN z y x sdotsdotsdotsdot

=

++minus ][23

3

222

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1754

0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

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Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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0 500 1000 1500 2000 25000

0001

0002

0003

00035

0

F1 u( )

m1minus

ssdot

F2 u( )

m1minus

ssdot

F3 u( )

m1minus

ssdot

25000 u

m s

1minus

sdot

3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Low T

High T

Mcad

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2154

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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3D Maxwell-Boltzmann Distribution3D Maxwell-Boltzmann Distribution

Conversion of Velocity-distribution to Energy-distribution

ε = frac12 m u2 d ε = mu du

2223

3

4 ua

u D

euadu

N dN sdotminus

minussdotsdotsdot=

π

kT

D

ekT d

N dN ε

ε

ε π ε

minus

minus

sdotsdot

sdot=

21

23

3

12

822019 Boltzmann Concept

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Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 1954

Velocity Values from M-B DistributionVelocity Values from M-B Distribution

bull urms = root mean square velocity

bull uavg = average velocity

bull ump = most probable velocity

int

sdot=

x

naverage

n

N dN x x )(

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull urms = root mean square velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull uavg = average velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2254

Velocity Value from M-B DistributionVelocity Value from M-B Distribution bull ump = most probable velocity

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2354

Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2454

Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2554

Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2654

Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2854

Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Comparison of Velocity ValuesComparison of Velocity Values

Ratio in terms of

urms uavg ump

173 160 141

m

kT

m

kT sdot3

m

kT sdot

π

8

m

kT sdot2

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Application to other Distribution FunctionsApplication to other Distribution Functions

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Collision Properties ( Ref Barrow )Collision Properties ( Ref Barrow )

bull ZI = collision frequency = number of collisions per molecule

bull λ = mean free path = distance traveled between collisions

bullZ

II= collision rate = total number of collisions

bull Main Concept =gt Treat molecules as hard-spheres

822019 Boltzmann Concept

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

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Collision Frequency ( ZI )Collision Frequency ( ZI )

Interaction Volume ( VI ) ( d = interaction diameter )

avg relative

avg I

uuwhere

ud V

sdot=

sdotsdotsdot=

2

2 2π

Define N = NV = molecules per unit volume

2

)()(

2 N ud Z

N V Z

avg I

I I

sdotsdotsdotsdot=

sdot=

π M

T R

m

T k uavg sdot

sdotsdot=

sdotsdotsdot

=π π

88

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Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

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Reaction ProgressReaction Progress

C lli i Th

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2754

Mean Free Path ( λ )Mean Free Path ( λ )

I

avg

Z

u==

timeunitinwithcollidesitmolecules

timeunitpertraveleddistanceλ

2

12

N d sdotsdotsdot= π λ

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2854

Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3154

Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

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httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Collision Rate ( ZII )Collision Rate ( ZII )

sdotsdot=

2

1 N Z Z I II

Double Counting Factor Double Counting Factor

22 )(2

1 N ud Z avg II sdotsdotsdotsdot= π

822019 Boltzmann Concept

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Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 2954

Viscosity ( η ) from Drag EffectsViscosity ( η ) from Drag Effects

λ η sdotsdotsdotsdot= m N uavg 2

1

2

12 N d sdotsdotsdot= π

λ

222 d

muavg

sdotsdot

sdot=

π η

123

100226

minus

sdot=

sdotsdot

=

mol L

T R

L P N

where

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3054

Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3154

Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

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822019 Boltzmann Concept

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Kinetic-Molecular-Theory Gas Properties - Collision Parameters

25oC and 1 atm

Species

Collision diameter Meanfree path CollisionFrequency CollisionRate

d 10-10 m d Aringλ 10-8

m

ZI 109 s-1 ZII 1034 m-3 s-1

H2 273 273 124 143 176

He 218 218 191 66 81 N2 374 374 656 72 89

O2 357 357 716 62 76Ar 362 362 699 57 70CO2 456 456 441 86 106

HI 556 556 296 75 106

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Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

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The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

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Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

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Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3154

Boltzmannrsquos Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

eua

du

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3254

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

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Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3354

The Arrhenius Equation

bull Arrhenius discovered most reaction-rate data obeyed theArrhenius equation

bull Including natural phenomena such asbull Chirp rates of crickets

bull Creeping rates of ants

Arrhenius ConceptArrhenius Concept

T R Ea

e Ak sdotminus

sdot=

A i i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

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httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3454

Extended Arrhenius EquationExtended Arrhenius Equation

2-32-121m where plusmn=sdotsdot= sdotminus T R

E meT ak

Experimentally m cannot be determined easily

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

Implication both A amp Ea vary quite slowly with temperatureOn the other hand rate constants vary quite dramatically withtemperature

E d d A h i E i

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httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

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822019 Boltzmann Concept

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mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

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Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

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Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3554

Extended Arrhenius EquationExtended Arrhenius Equation

T Rm E EaT ea A mm sdotsdot+=sdotsdot=

822019 Boltzmann Concept

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Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3654

Reaction ProgressReaction Progress

C lli i Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3754

Collision TheoryCollision Theory

Main Concept Rate Determining Step requires Bimolecular Encounter (ie collision)

Rxn Rate = (Collision Rate Factor) x (Activation Energy)

ZII (from simple

hard sphere collision properties)

ZII (from simple

hard sphere collision properties)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-BoltzmannDistribution)

822019 Boltzmann Concept

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Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3854

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

Fraction of molecules with E gt Ea e-EaRT (Maxwell-Boltzmann

Distribution)

C lli i Th lli i t ( Z )

C i i i i ( )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 3954

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

][)(2

1 22

avg II vvvd N Z equivsdotsdotsdotsdot= π

M

T R

m

T k v

sdotsdotsdot

=sdotsdotsdot

=π π

88

For A-B collisions micro AB vAB

AB

AB

B A

B A

AB

T k v

mm

mm

micro π

micro

sdot

sdotsdot=equiv gt

+

sdot

=equiv gt

8VelocityRelative

MassReduced

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

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Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

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Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

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Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

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Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4054

Collision DiameterCollision Diameter

2

B A AB

d d d

+=

Number per Unit VolumeNumber per Unit Volume

V

N

V

Ln N A A

A =sdot

=V

N

V

Ln N B B

B =sdot

=

Collision Theory collision rate ( Z )

C lli i Th lli i ( Z )

822019 Boltzmann Concept

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Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4154

Collision Theory collision rate ( ZII )Collision Theory collision rate ( ZII )

21

22)(

8)(

2

1

sdot

sdotsdotsdotsdot= A

A A AA II m

kT d N Z

π π

21

22)(

8

sdotsdotsdotsdotsdot=sdotsdotsdotsdot=

AB

AB B A AB AB B A AB II

kT d N N vd N N Z

micro π

π π

C lli i Th R t C t t C l l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4254

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Collision Theory

sdot= sdot

minusT R

Ea

II e Z )(Rate

Kinetics ][][)( 2 B A N N k sdotsdot=Rate

Combining Collision Theory with Kinetics

T R

Ea

B A

II e N N

Z k sdot

minussdot

sdot=

)()(2

C lli i Th R t C t t C l l ti

C i i C C i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4354

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-A Collisions

T R

Ea

A

Ae

m

T k d k sdot

minussdot

sdotsdotsdot

sdotsdotsdot=21

22

8

2

1

π π

m2 m s-1 per molecule

sdotsdot

mol

molecule

m

dm

1

100226

1

1023

3

33

T R

Ea

A

A AAe

m

T k d

Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot

=21

23

)(2

8

2

10

π π

Units of k dm

3

mol

-1

s

-1

equiv M

-1

s

-1

Collision Theor Rate Constant Calc lations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4454

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

A-B Collisions

T R

Ea

AB

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdot

sdotsdotsdotsdot=21

23)(2

810

micro π π

Units of k dm3 mol-1 s-1 equiv M-1 s-1

2

B A AB

d d d +=

B A

B A AB

mm

mm

+sdot= micro

Collision Theory Rate Constant Calculations

C lli i Th R C C l l i

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4554

Collision Theory Rate Constant CalculationsCollision Theory Rate Constant Calculations

Consider 2 NOCl(g) 2NO(g) + Cl2(g) T = 600 K

Ea = 103 kJmol d NOCl = 283 pm (hard-sphere diameter)

Calculate the second order rate constant

httpwwwubccaindexhtml

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4654

mass ratio k2 M s-1

Reaction Ea kJ mol-1

atom-1atom-2 atom-1 + atom-2-CO2----gt atom-1-atom-2 + CO2

-

1 120E+08 H + HCO2----gt H2 + CO2

-

05 230E+07 H + DCO2----gt HD + CO2

-

011 340E+06 Mu + HCO2----gt MuH + CO2

-33

0056 990E+05 Mu + DCO2----gt MuD + CO2

-39

Simple Collision Theory Comparison of MuoniumHydrogenDeuterium Abstractions

00E+00

20E+07

40E+07

60E+07

80E+07

10E+08

12E+08

14E+08

000 020 040 060 080 100

mass ratio

k M -

1 s

- 1

Transition State Theory

T iti St t Th

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4754

Transition State TheoryTransition State Theory

Concept Activated Complex or Transition State( Dagger )

3D Potential Energy Surface

Saddle point

H H

DD

H H

DD

H H

DD

H2 + D2 2 HD

H2 + D2 2 HD

Activated Complex or Transition State ( Dagger )

Potential Energy Surfaces

P t ti l E S f

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4854

Potential Energy SurfacesPotential Energy Surfaces

Consider D + H2 DH + H

D

HA HBr 2

r 1 θ r 1= dH-D

r 2 = dH-H

Most favorable at θ = 0o 180o

Calculate energy of interaction at different r 1 r 2 and θ Get

3D Energy Map

Reaction coordinate = path of minimum energy leading from

reactants to products

Reactions in Solutions

R ti i S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 4954

Reactions in SolutionsReactions in Solutions

Compared to gaseous reactions reactions insolutions require diffusion through the solventmolecules

The initial encounter frequencies should be

substantially higher for gas collisions

However in solutions though initial encounters

are lower but once the reactants meet they gettrapped in ldquosolvent cagesrdquo and could have agreat number of collisions before escaping thesolvent cage

Diffusion Controlled Solutions

Diff i C t ll d S l ti

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5054

Diffusion Controlled SolutionsDiffusion Controlled Solutions

Smoluchowski (1917) D = diffusion coefficient

)(4 B A ABdiff D D Ld k +sdotsdotsdotsdot= π

a

T k D

sdotsdotsdotsdot

=η π 6

η sdotsdotsdot

=3

8 T Rk diff

a = radius

η =viscosity

Diffusion Controlled (Aqueous) Reactions

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5254

Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5154

Diffusion Controlled (Aqueous) Reactions

viscosity η

η25C

08904103minus

sdot kg m1minus

sdot s1minus

sdot= η95C

02975 103minus

sdot kg m1minus

sdot s1minus

sdot=

T1 25 27315+( ) K sdot=k

8R Tsdot

3 ηsdot R 83145 Jsdot mol1minus

sdot K 1minus

sdot=T2 95 27315+( ) K sdot=

k 25C8 R sdot T1sdot

3 η25Csdot

= k 95C8 R sdot T2sdot

3 η95Csdot

=

k 25C 742 109

times L mol1minus

sdot s1minus

sdot= k 95C 274 1010

times L mol1minus

sdot s1minus

sdot=

Arrhenius Equation k A e

Eaminus

R Tsdotsdot kJ 10

3Jsdot=

EaR minus T1sdot T2sdot

T2 T1minusln

k 25C

k 95C

sdot=

Ea 17 104

times J mol1minus

sdot= Ea 17kJ mol1minus

sdot=

Therefore all aqueous solutions whose rate is determined by the

diffusion of species should have an Activation Energy of about 17kJmol

Diff-paper

Quantum Mechanical Tunneling

Q t M h i l T li

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

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Quantum Mechanical TunnelingQuantum Mechanical Tunneling

)(22

14

E Eam L

e E

Ea

E

Eaminussdotsdot

minussdot

minussdot

sdot=Tunnelingof Prob

bull curvature in Arrhenius plots

bull abnormal A-factors

bull relative isotope effects

bull low Ea

Boltzmannrsquos Concepts of Reaction Rates

Bolt mannrsquos Concepts of Reaction Rates

822019 Boltzmann Concept

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Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

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Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5354

Boltzmann s Concepts of Reaction RatesBoltzmannrsquos Concepts of Reaction Rates

V e l o c

C o l l i s i o M e a n V i s c o

D e r i v E n e r g

M a x w e l l - B o

B a r o m e t r i

B o l t z m a n

2223

3

4 ua

D

euadu

N dN sdotminussdotsdotsdot=

π

int

sdot= x

naverage

n

N

dN x x )(

Theories of Reaction Rates

Th i f R ti R t

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff

822019 Boltzmann Concept

httpslidepdfcomreaderfullboltzmann-concept 5454

Theories of Reaction RatesTheories of Reaction Rates

C o l l i s i o

P o t e n t i a

U n i m o l e

M u o n i

Q M T

I s o t o p

R e a c t i o D i f f u s i o

P a r t i t i o

T r a n s i t i o T D T r e a

C o l l i s i o H a r d S p

A r r h e n i

T R

Ea

AB ABe

T k d Lk sdot

minussdot

sdotsdotsdotsdotsdotsdot=

21

23

)(2

810 π

η sdot sdotsdot= 38 T Rk diff