Thermo-chemistry

Calculate the volume of gas released at 227oC

under 83.1 kPa pressure when 16 kg of NH4NO3 is exploded forming N2,

O2, & H2O:

Thermo-chemistry

Thermochemistry

•The study of heat transfer in

chemical reactions

Thermochemistry•Heat change

•Calorimetry

•TCE

Thermo-chemical

Terms

System

•That part of nature upon which

attention is focused

Surroundings•That part of nature

around the part upon which we are

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

Endothermic Rxn

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

Heat Change

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

•C: (J/goC, J/kgoK)

Sp. Heat

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

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.

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

Drill: Calculate the heat required to change 25 g

of water from 140.0oC to 60.0oC

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

Calorimetry•Experimental measure of heat transfer

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)H = q = the heat or enthalpy change in a system

Hsys = mCTsys parts

CalorimetryHsystem = 0

Hsys = Hcal + Hrxn

Hrxn = -Hcal

Hrxn = -mCTcal

When Q reacts in a 1.5 kg calorimeter containing 2.5

kg water ch. from 22.5oC to 26.5oC. Calculate Hrxn.

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

When X reacts in a 2.0 kg calorimeter containing 1.5 kg water went from 22.5oC to 30.5oC. Calculate Hrxn.

Cwater = 4.18 J/gK Ccal = 1.50 J/gK

Homework•Problems 7 & 8

•On page 234

Thermo-chemical Equation

Terms

Typical Reaction

•HCl + NaOH NaCl + HOH

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

Hrxn

Typical Ionization

HCl

H+(aq) + Cl-

(aq)

Heat of Solution

•The heat or enthalpy change when a substance is dissolved

Hsoln

Combustion Reaction

•CxHy + O2

CO2 + HOH

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

Hcombustion

Rxn Making Cpds from ele

H2 + ½ O2 H2O

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

Hfo (kJ/mole)

The Degree Symbol•Indicates standard conditions & molar

quantities by itself or from a balanced

equation.

Enthalpy•Heat flow in a

system

H

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

•Determines spontaneity

G

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

Gfo (kJ/mole)

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

Entropy•A measure of disorder

So

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

•Sfo (J/moleoK)

Drill: Define:• Heat of reaction

• Heat of solution

• Heat of formation

• Energy of formation

• Entropy of formation

Thermochemical Equation

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

Drill: Identify type of rxn when:

G > 0G < 0G = 0

Thermochemical Equation

Ho

rxn Hf

o

productsHf

o

reactants

Thermochemical Equation

Go

rxn Gf

o

productsGf

o

reactants

Thermochemical Equation

So

rxnSf

o

products

Sfo

reactants

Thermochemical Equation

•Stoichiometry of heat change

•Solves theoretical yield

Interrelating Equation

GH

S

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 112.1 213.6 70.4

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

into CaO + SO2 + O2 at 27oC

Cmpd CaSO4 SO2 CaO

Hf

o -1434.1 -296.8 -635.1

Gf

o -1321.8 -300.2 -604.0

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 when P + QR PR2 + Qat -23oC & Teq

Compd QR PR2

Hfo(kJ/mole) -250 -450

Gfo(kJ/mole) -225 -425

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

Lab Results: Cup H2O NaOH Thermo

5.0 g 50.0 g 4.0 g 15.0 g Ti = 22.0

oC Tf = 27.0

oC

Cmpd NaOH Na+ OH-

Hf

o -425.6 -240.1 -230.0

Determine: theoretical and experimental heat changes

When 2.00 g NaOH dissolves in a 1.0 L water in a 2.5 kg calorimeter, the temp. went

from 22.5oC to 26.5oC. Calculate: Ho

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

Bond Energy•The energy change

when one mole of bonds are broken

Ho

bond

Bond Equation

Hbondo

rxnHbond

o

products

Hbondo

reactants

Bond Energies (kJ/mole)

C-C 347

C-H 414

O-H 464

C=O 715

Drill:Calculate H, G, & S in the production of 831mL

ammonia at 227oC under

250.0 kPa pressureCompd NH3

Hfo -46.1

Gfo -16.5

HOLY MACKERAL

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

Calculate Ho, Go, & S when A + BC AC2 + Bat -23oC & solve Teq

Compd BC AC2

Hfo(kJ/mole) -150 -250

Gfo(kJ/mole) -125 -225

Hess’s LawHrxn is the same

whether it occurs in a single step or a series

of steps.

Calculate Ho, Go, & S when A + BC AC + Bat -23oC & Teq

Compd BC ACHf

o(kJ/mole) -150 -250Gf

o(kJ/mole) -175 -225

Write TE for the process2 A + B C + D

C + A H

D + B 2 K

H + K M + B

K + M Product

Write TE for the process2 A + B C + D

C + A H

D + B 2 K

H + K M + B

K + M 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: When 5.00 g NsCO3 is decomposed to NsO & CO2 in a 500.0 g calorimeter (C = 1.50 J/gK) containing 250 g of water (C = 4.18 J/gK), the water changes from 25.00oC to 45.00oC. Calculate the heat of rxn/mole of NsCO3

Substance Hof(kJ.mole)

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

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

C + A 2 H + P

D + B 2 K + P

H + K P + Q

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, 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

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

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

What does each symbol represent?

Define what is represents:

H:G:S: