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Transcript of Boltzmann Concept
822019 Boltzmann Concept
httpslidepdfcomreaderfullboltzmann-concept 154
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
822019 Boltzmann Concept
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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
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
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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
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
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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
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 )(
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
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 )
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
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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
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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
httpslidepdfcomreaderfullboltzmann-concept 254
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
822019 Boltzmann Concept
httpslidepdfcomreaderfullboltzmann-concept 354
PS 5
822019 Boltzmann Concept
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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
822019 Boltzmann Concept
httpslidepdfcomreaderfullboltzmann-concept 554
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
822019 Boltzmann Concept
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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
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
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
822019 Boltzmann Concept
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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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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
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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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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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
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
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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
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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
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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
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
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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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
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
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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 )(
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
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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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
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
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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
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
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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
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
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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
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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
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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
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
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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
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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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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
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
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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 ( )
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
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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
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
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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
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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
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
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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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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
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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
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
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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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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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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
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
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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
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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
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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 )
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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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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
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
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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
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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
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
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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
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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
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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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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
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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
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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
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 )
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
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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
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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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
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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
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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
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
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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 )
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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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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
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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
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
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
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
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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
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
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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
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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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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
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
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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
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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
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
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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
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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
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
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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
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
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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
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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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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
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
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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
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
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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
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
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
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 ( )
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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
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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
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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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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
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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
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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
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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
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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
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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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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
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
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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
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
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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
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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
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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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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
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
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
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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)
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 ( )
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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
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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
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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
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
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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
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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
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
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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
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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
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
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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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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
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
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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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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
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
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 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
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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
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
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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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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
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 )
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
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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
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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
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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 ( )
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
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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
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
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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
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
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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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
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 )
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
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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
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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 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
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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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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
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
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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
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
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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
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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
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
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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
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
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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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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
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 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
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
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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
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
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
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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
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 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
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
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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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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=
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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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
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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
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
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
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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
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
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
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 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 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
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 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 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