Thermo- chemistry. Thermochemistry The study of heat transfer in chemical reactions.

Thermo-chemistry

Thermochemistry

•The study of heat transfer in

chemical reactions

Thermo-chemical

Terms

Heat (H)•A form of energy

that can flow between samples of

matter

Heat cannot be measured directly; thus, we measure heat change (H)

Enthalpy Change•Heat that can flow in/out of a system

H

System•That part of nature upon which attention

is focused

Surroundings•That part of nature

which we are not focused

Reaction Coordinate

•A graph of energy change versus time in a chemical reaction

Time

Ene

rgy

RP

Exothermic Rxn•Chemical reactions

that release, give off heat, or lose

heat

Exothermic Rxn•Products will

contain less heat than the reactants

H < 0

Endothermic Rxn

•Chemical reactions that absorb, take in heat, or gain heat

Endothermic Rxn•Products will

contain more heat than the reactants

H > 0

Thermochemistry Topics

•Heat Change

•Calorimetry

•Thermochemical Equation

Topic: Heat

Change

Specific Heat•The heat required to raise one gram of a substance 1oC

•c: (J/goC, J/kgK)

Specific Heat Formula

H = mcT

Heat of Fusion•The heat required to melt one gram of a substance at its normal MP

•Hf: (J/g or J/kg)

Heat of Fusion Formula

H = mHf

Heat of Vaporization

•The heat required to boil one gram of a substance at its normal BP

•Hv: (J/g or J/kg)

Heat of Vap. Formula

H = mHv

Calculate the heat change when 10.0 g H2O goes from –100.0oC to 200oC.MP = 0oC BP = 100oCHf = 334 J/g HV = 2260 J/g

cice = 2.06 J/gKcwater = 4.18 J/gK csteam = 2.02 J/gK

Calculate the heat change when 5.00 g H2O goes from –10.0oC to 120oC.MP = 0oC BP = 100oCHf = 334 J/g HV = 2260 J/g

cice = 2.06 J/gKcwater = 4.18 J/gK csteam = 2.02 J/gK

Topic:

Calorimetry

Calorimetry•A study of how to

measure experimental heat

transfer in a system

Calorimeter•Device used to measure heat transfer

•A calorimeter is an adiabatic system

•Experimental yield

Adiabatic System•A system that exchanges zero heat with its surroundings

Hsystem = 0

H (J or kJ)H ~ q = the heat or enthalpy change in a system

Hsys = Hsys parts

CalorimetryHsystem = 0

Hsys = Hcal + Hrxn

Hrxn = -Hcal (all parts)

Hrxn = -mcTcal (all)

When Q reacts in a 1.5 kg calorimeter containing 2.5 kg water the temp changes from

22.50oC to 26.50oC.Calculate Hrxn. Cwater = 4.18 J/gK Ccal = 2.00 J/gK

In expensive calorimeters, the mass is constant; thus, the mc can be calculated together as C (J/oC).

Hrxn = -mcTcal

Hrxn = -CTcal

When X reacts in a 2.0 kg calorimeter containing 1.5 kg water, the temp changes

from 22.5oC to 30.5oC. Calculate Hrxn. Cwater = 4.18 J/gK Ccal = 1.50 J/gK

When X reacts in a 2.0 kg calorimeter containing 2.0 kg

water, T = 20.0oC to0.0oC. Calculate Hrxn.

50.0 % freezes.Hf = 334 J/g

Cwater = 4.18 J/gK Ccal = 2.00 J/gK

When 40.0 g NH4NO3 dissolves in 460.0 g water at 25.0oC, the temp. falls to 22.5oC. Calculate the Ho

per mole of NH4NO3.csoln = 4.00 J/gK

Topic:Thermochemical

Equation (TCE)

Thermo-chemical Equation

Terms

Heat of Reaction•The heat or enthalpy change of a chemical reaction

Hrxn

Typical Reaction

•HCl + NaOH NaCl + HOH

Heat of Solution

•The heat or enthalpy change when a substance is dissolved

Hsoln

Typical Ionization

KCl

K+(aq) + Cl-

(aq)

Heat of Combustion•The heat or enthalpy change when a substance is burned

Hcombustion

Combustion Reaction

•CxHy + O2

CO2 + HOH

Heat of Formation•The heat required to form one mole of a compound from pure elements

Hfo (kJ/mole)

Rxn Making Cpds from ele

H2 + ½ O2 H2O

The Degree Symbol•Indicates standard conditions & molar

quantities by itself or from a balanced

equation.

Gibb’s Free Energy•Energy of a system that can be converted to work

•Determines spontaneity

G

Exergonic Reaction•A reaction in which free energy is given off

G < 0

Endergonic Reaction

•A reaction in which free energy is absorbed

G > 0

Exergonic Reaction•A reaction which can be spontaneous

G < 0

Endergonic Reaction

•A reaction which cannot be spontaneous

G > 0

Reaction at Equilibrium

G = 0

Interrelation Term (G)

G interrelates thermochemistry,

chemical equilibria,

& electrochemistry

Energy of Formation•The energy required to form one mole of a compound from pure elements

Gfo (kJ/mole)

Entropy•A measure of disorder

S (J/K)

Entropy of Formation•The entropy of one mole of a substance

•Sfo (J/moleK)

•Sfo (kJ/moleK)

Thermochemical Equation

•An equation that shows changes in heat, energy, etc


Ho

rxn Hf

o

productsHf

o

reactants


Go

rxn Gf

o

productsGf

o

reactants


So

rxnSf

o

products

Sfo

r

eactants


•Stoichiometry of heat change

•Solves theoretical yield


•The 3rd step in stoichiometry involves converting what’s given to what’s asked for.


•Use the TCE for the 3rd step of stoichiometry to convert moles given to heat or free energy.

In stoichoimetric calculations, the TCE

is used for the conversion from mole

to heat, energy, or entropy.

Interrelating Equation

GH

S


Xo

rxn Xf

o

productsXf

o

reactants

Interrelating Equation

GH

S

Calc. H, G, & S when 13.6 g of CaSO4 is changed

into CaO + SO2 + O2 at 25oC

Cmpd CaSO4 SO2 CaO

Hf

o -1434.1 -296.8 -635.1

Gf

o -1321.8 -300.2 -604.0

Calculate H, G, & S when 19.7 kg of BaCO3 is decomposed into BaO + CO2

Cmpd BaCO3 CO2 . BaO

Hf

o -1216.3 -393.5 -553.5

Gf

o -1137.6 -394.4 -525.1

Sf

o

Drill: Calculate Ho

rxn &Go

rxn for:A + B2C3 AC2 + B

Compd B2C3 AC2

Hfo(kJ/mole) -150 -250

Gfo(kJ/mole) -175 -225

Calculate Ho, G

o, & S for

AD2 + BC AC2 + BD

at (-23oC)

Cpd BC AD2 AC2 BD

Hf

o -150 -250 -300 -175

Gf

o -125 -225 -250 -150

Sf

o 75 50 80 ?

Determine Sf

o

BD

Drill: Calculate Ho, Go, & So when P + QR PR2 + QCompd QR PR2



Ccup = 0.50 J/gK Cwater = 4.18 J/gK CNaOH = 1.00 J/gK

CThermometer = 2.00 J/gK

Required Constants

Lab Results: Cup H2O NaOH Thermo

5.0 g 50.0 g 2.0 g 20.0 g Ti = 22.0

oC Tf = 30.0

oC

Cmpd NaOH Na+ OH-

Hf

o -426.7 -240.1 -230.0

Determine: theoretical and experimental heat changes

Calculate the potential Ho, Go, & So for the reaction involving the burning of C3H8 Cpd C3H8 CO2 H2O

Hf

o-103.8 -393.5 -241.8

Gf

o- 23.5 -394.4 -228.6

Calculate the potential H, G, & S for the reaction & Sf

o for

O2 when burning 8.8 kg of C3H8 Cpd C3H8 CO2 H2O

Hf

o-103.8 -393.5 -241.8

Gf

o- 23.5 -394.4 -228.6

Sf

o269.9 213.6 188.7

Calculate Ho, Go, S, & at -23oC when: A + BC AC + B

Compd BC ACHf

o(kJ/mole) -150 -250Gf

o(kJ/mole) -175 -225

Drill: When 35.0 g NaOH dissolves in 965 mL water in a 2.5 kg calorimeter, the temp. went from 22.5oC to 26.5oC. Calculate: Ho

soln Csoln = 4.00 J/gK Ccal = 2.00 J/gK

TestReview

Calculate Ho, Go, & S at 227

oC for the production of

ammonia from N2 & H2.

Compd NH3

Hfo -46.1

Gfo -16.5

When 25.0 g CaCO3 is made

from CaO & CO2 in a 500. g calorimeter (C = 1.50 J/gK) containing 250.0 g of water

(C = 4.18 J/gK), the system changes from 25.0oC to 45.0oC. Calculate Hrxn/mole of CaCO3

Heat Change•Calculate the heat change when the temperature of 1.0 kg H2O is changed from –100.0oC to 200.0oC.

Bond Energy•The energy change

when one mole of bonds are broken

Ho

bond

Bond Equation

Hbondo

rxnHbond

o

products

Hbondo

reactant

s)

Bond Energies (kJ/mole)

C-C 347 O=O

C-H 414 498

O-H 464

C=O 715

Calculate the heat change when 1.00

mole of C2H6 is burned.

1st Law Thermodynamics

•Total energy change = heat + work

E = q + W

Work•W = Fd

•P = F/A

•V = Ad

•W = PV = nRT

2nd Law Thermodynamics

•Total entropy in a system always increases assuming no energy is added to the system

Thermodynamic Rxns are State

Rxns

State Reaction•Reactions that are independent of the

path; thus not dependent on intermediates

Drill: Calculate Ho, Go, & So when:

A + BC AC2 + BCompd BC AC2



Hess’s LawHrxn is the same

whether it occurs in a single step or a series

of steps.

Write TE for the process2 A + B C + D

C + A H

D + B 2 K

H + K M + B

K + M Product

2 A + B C + D

C + A H

D + B 2 K

H + K M + B

K + M Product

3 A + B Product

Write TE for the process2 A + 2 B C + D

C + A 2 H

D + B 2 K

H + K P + B

Write TE for the process2 A + 2 B C + D

C + A 2 H

D + B 2 K

2 H + 2 K 2 P + 2 B

Drill: Calculate Horxn for

the production of CaCO3 from CaO & CO2

Hf

o

(kJ/mole)

CaCO3 CaO CO2

-1206.9 -635.1 -393.5

Calculate the % yield from the

results of the last two slides

Bond Equation

Hbondo

rxnHbond

o

products

Hbondo

reactant

s)

Bond Energies (kJ/mole)

C-C 347 O=O

C-H 414 685

O-H 464

C=O 715

Calculate the heat change when 6.0

kg of ethane (C2H6) is burned

in excess oxygen.

Substance Hof(kJ/mole)

S Hof S Ho

f

A -100 H -150B -150 K -200C -50 P -250D -125 Q -300

Solve Horxn for TE

A + B 2 C + 2 D

C + A 2 H + P

D + B 2 K + P

H + K P + Q

Solve Horxn for TE

A + B 2 C + 2 D

2C + 2A 4 H + 2P

2D + 2B 4K + 2P

4H + 4K 4P + 4Q

Test on Thermochemistry

Tomorrow

Review

Calculate Htotal, when 40.0 g of

H2O is changed from - 25oC to

125oC. FPw = 0.0oC

BPw = 100.0 oC Hv = 2260 J/gCice = 2.06 (J/g K) Hf = 334 J/gCwater = 4.18 (J/g K)Csteam = 2.02 (J/g K)

Calculate Ho, Go, & So for N2O5 + H2O HNO3

Cpd N2O5 H2O HNO3 Hf

o -11.3 -285.8 -174.1

Gfo -10.4 -237.2 -151.5

When 10.8 g N2O5 is added to a

1.50 kg calorimeter (C = 1.00 J/gK) containing 1.00 kg of H2O

(C = 4.18 J/gK), the N2O5reacts with the water forming HNO3.

The temp. of the system changes from 23.000oC to 23.750oC.

Calculate the Hrxn/mole N2O5.

Calculate the % yield of the

reaction in the last two slides.

Solve Ho for TE X + Y 2 W + 2 Z 60 kJ

W + X 2 R + P 40 kJ

2 S + P Z + Y 50 kJ

R + S P + Q 80 kJ

Ho for TE X + Y 2 W + 2 Z 60 kJ

2W + 2X 4 R + 2P 80 kJ

2Z + 2Y 4 S + 2P -100 kJ

4 R + 4S 4P + 4Q 320 kJ

3X + 3Y 8P + 4Q 360 kJ

Calculate Ho, Go, & So for PbO2 + CO CO2 + Pb

Cpd PbO2 CO CO2 Hf

o -277.4 -110.5 -393.5

Gfo -217.4 -137.2 -394.4

Calculate: Teq & H of 48 g PbO2

Test Tomorrow

When 4.20 g MgCO3 is decomposed to MgO & CO2 in a 2500.0 g calorimeter (C = 2.00 J/gK) containing 1.0.kg of water (C = 4.18 J/gK), the water changes from 23.00oC to 13.00oC. Calculate the heat of rxn/mole of MgCO3

Thermo- chemistry. Thermochemistry The study of heat transfer in chemical reactions.

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Transcript of Thermo- chemistry. Thermochemistry The study of heat transfer in chemical reactions.