Name:________________________________
_____
Chemistry 30
Thermochemistry Workbook
Heat Calculations
1. Calculate the quantity of heat required to warm 250 mL of water from 22.0C to 98.0C in
an electric kettle. Note: water has a density of 1 g/mL 1 mL has a mass of 1 g.
2. A 35.0 g polystyrene foam cup containing coffee changes in temperature from 21.0C to
55.0C. Calculate the heat absorbed by the cup.
3. What mass of aluminum in a car engine will absorb 1.00  106 J of heat when the
temperature rises from 22C to 102C after the car is started?
4. The liquid coolant in a car engine has a specific heat capacity of 3.88 J/gC. Determine the
mass of coolant that will absorb 1.00 MJ of heat during a temperature rise from 22C to
102C.
5. In a laboratory experiment, 2.00 kJ of heat flowed to a 100 g sample of a liquid solvent,
causing a temperature increase from 15.40C to 21.37C. Calculate the specific heat
capacity of the liquid solvent.
6. A human body loses about 360 kJ of heat every hour. Assuming that an average human
body is equivalent to about 60 kg of water, what temperature decrease would this heat
transfer cause?
Energy Changes
Part I
Rewrite the following equations expressing the balanced equation with one mole of the
substance underlined and using the rH notation. Sketch a labelled potential energy diagram
for each question.
Example
2 H2O(l) + 571.6 kJ  2 H2(g) + O2(g)
Answer:
H2O(l) 
H2(g) +
1
2
O2(g) rH = + 285.8 kJ
H2(g) +
EP
(kJ)
1
2
O2(g)
rH = +285.8 kJ
H2O(l)
Reaction Progress
Chem 30 Thermochemistry Workbook
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Jill Agnew
1.
N2(g) + O2(g) + 180.8 kJ  2 NO(g)
2.
2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g) + 2857 kJ
3.
2 Na(s) + 218 kJ  2 Na(g)
Part II
Rewrite the following equations to have the simplest whole number coefficients and by
expressing the energy change as a term in the equation. Sketch a labelled potential energy
diagram for each question.
Example
Mg(s) + 1 2 O2(g)  MgO(s)
rH = -601.6 kJ
Answer:
2 Mg(s) +
O2(g)  2 MgO(s) + 1203.2 kJ
2 Mg(s) +
O2(g)
EP
(kJ)
rH = 1203.2 kJ
2 MgO(s)
Reaction Progress
O2(g)  Al2O3(s)
1.
2 Al(s) +
2.
H2SO4(l)  SO2(g) + H2O(g) +
3.
NH3(g) 
3
2
1
2
rH = 1680.0 kJ
1
2
O2(g)
rH = +273.0 kJ
rH = +46.1 kJ
N2(g) + 3/2 H2(g)
Enthalpy Changes
1. Given the reaction 3 NO2(g) + H2O(l)  2 HNO3(l) + NO(g) rH = 72.0 kJ,
calculate the molar enthalpy of reaction, rH for:
a) NO2(g)
b) H2O(l)
c) HNO3(l)
d) NO(g)
2. The molar enthalpy of combustion of butane is 2657.3 kJ/mol. Calculate the enthalpy
change when:
a) 2.50 mol of butane burns.
b) 5.00 mol of butane burns.
c) What is the relationship between a) and b)?
3. Calculate the heat released (enthalpy change) when 100 g of methane is burned in a water
heater. cH = 802.5 kJ/mol CH4(g).
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Jill Agnew
4. Calculate the molar enthalpy of combustion for octane, C8H18(l) if the combustion of
10.00 g releases 444.0 kJ of energy.
5. Calculate the enthalpy change when 5.00 g of glucose is burned during cellular respiration.
The molar enthalpy of reaction for glucose is 2802.5 kJ/mol.
6. Calculate the heat released when 3.40 kg of oxygen is used when propane burns in a gas
BBQ. The molar enthalpy of reaction for oxygen is 408.8 kJ/mol.
7. What mass of ethane is required to produce 1500 kJ of energy during a combustion
reaction? The molar enthalpy of combustion of ethane is 1251.0 kJ/mol.
Calorimetry
1. Calculate the heat lost in a chemical reaction which causes 250 g of water to increase in
temperature by 12.0C.
2. A chemical reaction in a bomb calorimeter causes the temperature of 1470 g of water to
decrease in temperature from 27.70C to 18.00C. Calculate the heat gained by the
reaction.
3. The combustion of 0.500 g of carbon causes the temperature of 100 mL of water in a bomb
calorimeter to rise from 20.10C to 59.20C. Calculate the molar enthalpy of combustion
of carbon in kJ/mol.
4. A 12.7 g sample of sulphur, S8(s), is placed in a bomb which is then filled with oxygen
under pressure. The bomb is placed in the calorimeter which is filled with 2.20 kg of water
at 21.08C. The reaction mixture is ignited and the temperature rises to 33.88C.
Calculate the molar heat of combustion of sulphur in kJ/mol.
5. A student mixed 100.0 mL of 1.50 mol/L sulphuric acid with 200.0 mL of 1.50 mol/L
sodium hydroxide. Both solutions were at 19.67C initially and the highest temperature
reached by the reaction mixture was 34.06C. Calculate the molar enthalpy of
neutralization for sulphuric acid in kJ/mol.
6. Calculate the molar enthalpy of combustion of octane when 0.530 g is burned in a
calorimeter. The temperature of both the 13.0 g aluminium coffee can calorimeter and the
250 mL of water increased by 17.2C. Convert to kJ/g.
7. Calculate the molar enthalpy of combustion of butane if 1.22 g of the fuel increased the
temperature of a tin can calorimeter (22.5 g of tin and 200 mL of water) by 8.30C.
Convert to kJ/g.
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Jill Agnew
Industrial Bomb Calorimeters
1. A calorimeter has a heat capacity of 40.00 kJ/C. Complete combustion of 1.00 g of
hydrogen in this calorimeter causes a temperature increase of 3.54C. Calculate the molar
enthalpy of combustion for hydrogen.
2. Combustion of 3.50 g of ethanol in a calorimeter with a heat capacity of 15.2 kJ/C causes
a temperature increase from 19.88C to 26.18C. Find the molar enthalpy of combustion
for ethanol from this evidence.
3. A 16.0 g sample of peanut butter is placed in a bomb calorimeter that has a heat capacity of
8.28 kJ/C. The initial temperature of the calorimeter is 25.0C and the final maximum
temperature after the peanut butter sample has been burned is 75.5C. Calculate the
enthalpy of combustion of the peanut butter in kJ/g.
Hess’s Law – Additivity of Reaction Heats
1. Determine the heat of reaction for:
C(s) + 2 H2(g)  CH4(g)
H2(g) +
1
2
O2(g)  H2O(l)
H = 285.8 kJ
C(s) + O2(g)  CO2(g)
H = 393.5 kJ
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l)
H = 890.5 kJ
2. Determine the heat of reaction for:
C(s) + H2O(g)  CO(g) + H2(g)
H2(g) +
1
2
O2(g)  H2O(g)
H = 241.8 kJ
C(s) + O2(g)  CO2(g)
CO(g) +
1
2
H = 393.5 kJ
O2(g)  CO2(g)
H = 283.0 kJ
3. Determine the heat of reaction for:
2 C(s) + 2 H2(g) + O2(g)  CH3COOH(l)
H2(g) +
1
2
O2(g)  H2O(l)
H = 285.8 kJ
C(s) + O2(g)  CO2(g)
H = 393.5 kJ
CH3COOH(l) + 2 O2(g)  2 CO2(g) + 2 H2O(l)
H = 874.3 kJ
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Jill Agnew
4. Determine the heat of formation for carbon monoxide:
C(s) + 1 2 O2(g)  CO(g)
C(s) + O2(g)  CO2(g)
CO(g) +
1
2
O2(g)  CO2(g)
5. Determine the heat of reaction for:
2 NO2(g)  2 NO(g)
1
1
2
2
H = 393.5 kJ
N2(s) +
1
2
H = 283.0 kJ
+ O2(g)
O2(g)  NO(g)
H = +91.3 kJ
N2(s) + O2(g)  NO2(g)
H = +33.2 kJ
6. Determine the heat of reaction for the formation of silver chloride from its elements:
H2(g) +
1
2
1
2
O2(g)  H2O(l)
H2(g) +
2 Ag(s) +
1
1
2
2
H = 285.8 kJ
Cl2(g)  HCl(g)
H = 92.3 kJ
O2(g)  Ag2O(s)
H = 30.6 kJ
Ag2O(s) + 2 HCl(g)  2 AgCl(s) + H2O(l) H = 324.6 kJ
7. Calculate the heat of formation of iron (III) oxide from iron and oxygen given the following
data:
3 C(s) + 2 Fe2O3(s)  4 Fe(s) + 3 CO2(g)
H = 481.0 kJ
C(s) + O2(g)  CO2(g)
H = 393.5 kJ
H = kJ
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Jill Agnew
Hess’s Law – Additivity of Reaction Heats
Given Reactions
H2(g) +
1
H2(g) +
1
2
O2(g)  H2O(g)
ΔH = 241.8 kJ
2
O2(g)  H2O(l)
ΔH = 285.8 kJ
S(s) + O2(g)  SO2(g)
ΔH = 296.8 kJ
H2(g) + S(s) + 2 O2(g)  H2SO4(l)
ΔH = 814.0 kJ
1
1
1
O2(g)  NO(g)
2
N2(g) +
2
N2(g) + O2(g)  NO2(g)
2
N2(g) +
C(s) +
1
1
3
2
ΔH = +91.3 kJ
ΔH = +33.2 kJ
H2(g)  NH3(g)
2
ΔH = 45.9 kJ
O2(g)  CO(g)
2
ΔH = 110.5 kJ
C(s) + O2(g)  CO2(g)
ΔH = 393.5 kJ
C(s) + 2 H2(g)  CH4(g)
ΔH = 74.6 kJ
2 C(s) + 3 H2(g)  C2H6(g)
ΔH = 84.0 kJ
3 C(s) + 4 H2(g)  C3H8(g)
ΔH = 103.8 kJ
1
2
H2(g) +
S(s) +
3
2
1
I2(g)  HI(g)
2
ΔH = +26.5 kJ
O2(g)  SO3(g)
ΔH = 395.7 kJ
2 C(s) + 2 H2(g) + O2(g)  CH3COOH(l)
ΔH = 484.3 kJ
Calculate the heat of reaction (ΔH) using Hess’s Law and the given reactions for each of the
following reactions:
1. NO(g) + 1 2 O2(g)  NO2(g)
ΔH = ?
2. CO(g) +
1
2
O2(g)  CO2(g)
ΔH = ?
3. CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(g)
4. NH3(g) +
7
4
O2(g)  NO2(g) +
3
2
ΔH = ?
H2O(g)
5. H2O(l)  H2O(g)
6. SO2(g) +
1
2
ΔH = ?
ΔH = ?
O2(g)  SO3(g)
ΔH = ?
7. SO3(g) + H2O(l)  H2SO4(l)
ΔH = ?
8. H2O(g) + C(s)  CO(g) + H2(g)
ΔH = ?
9. 3 CH3COOH(l) +
11
2
O2(g)  5CO2(g) + CO(g) + 6 H2O(g)
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ΔH = ?
Jill Agnew
Hess’s Law – Heats of Formation
1. Using the fH values in your Data Booklet, calculate the heat of reaction (enthalpy change)
for each of the following and draw the potential energy (EP) diagram:
a) Fe2O3(s) + 3 CO(g)  3 CO2(g) + 2 Fe(s)
b) 4 NO2(g) + 6 H2O(g)  4 NH3(g) + 7 O2(g)
c) 2 CuO(s) + C(s)  2 Cu(s) + CO2(g)
d) 2 H2S(g) + 3 O2(g)  2 H2O(g) + 2 SO2(g)
e) 2 Al(s) + Fe2O3(s)  Al2O3(s) + 2 Fe(s)
2. Calculate the molar heat of reaction for acetic acid given the following equation.
6 CH3COOH(l) + 11 O2(g)  10 CO2(g) + 2 CO(g) + 12 H2O(g)
3. The molar heat of formation of TNT, trinitrotoluene is –35.4 kJ/mol. What is the molar
heat of decomposition of TNT according to the following reaction:
2 C7H5(NO2)3(s)  7 C(s) + 7 CO(g) + 3 N2(g) + 5 H2O(g)
4. Carbohydrates, such as sugars and starches, are oxidized in the body to provide needed
energy through cellular respiration. Calculate the molar heat of combustion for glucose
assuming that the products of combustion are carbon dioxide and liquid water.
5. Calculate the heat released when 150 g of ethanol burn in an alcohol burner.
6. Calculate the heat produced when 6.50  103 g of sulphur trioxide combines with water to
produce sulphuric acid.
7. In respiration, glucose is oxidized by oxygen gas to produce carbon dioxide gas, liquid
water and energy. What is the energy released when 18.0 g of glucose is consumed?
8. The enthalpy change for the combustion of one mole of glutaric acid, H2C5H6O4(s), is
–2154.0 kJ. Assuming that carbon dioxide and water vapour are produced, calculate the
molar heat of formation for glutaric acid.
9. Calculate the molar heat of formation for nitric acid given the following reaction:
3 NO2(g) + H2O(l)  2 HNO3(l) + NO(g) H = 72.0 kJ
10. The molar heat of combustion of toluene, C6H5CH3(l), is –3915.6 kJ/mol. Calculate the
molar heat of formation of toluene. The products of combustion are carbon dioxide and
water vapour.
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Jill Agnew
Extra Practice
1. Given the reaction for cellular respiration:
C6H12O6(s) + 6 O2(g)  6 CO2(g) + 6 H2O()
rH = 2802.5 kJ
Calculate the molar enthalpy of reaction for:
a) O2(g)
b) CO2(g)
c) H2O()
2. Cellular respiration is a combustion process used by our bodies to release the chemical
energy stored in glucose. Use cH = 2802.5 kJ/mol of glucose to calculate the enthalpy
change when:
a. 2.5000 mol of glucose burns
b. 100.00 mol of glucose burns
c. 100.00 g of glucose burns
d. 180.18 g of glucose burns
3. The combustion of 1.00 g of octane causes the temperature of 250 mL of water in a
calorimeter to rise from 15.00C to 69.00C. Calculate the molar enthalpy of
combustion of octane in kJ/mol. Convert to kJ/g.
4. A student mixed 50.0 mL of 0.250 mol/L phosphoric acid with 150.0 mL of 0.250
mol/L sodium hydroxide. Both solutions were at 22.15C initially and the highest
temperature reached by the reaction mixture was 36.25C. Calculate:
a) the molar enthalpy of neutralization for phosphoric acid in kJ/mol
b) the molar enthalpy of neutralization for sodium hydroxide in kJ/mol
5. A 15.8 g sample of white phosphorus, P4(s), is placed in a bomb calorimeter with a heat
capacity of 10.68 kJ/C. The initial temperature of the calorimeter is 23.05C. The
phosphorus is ignited and the temperature of the water rises to 34.70C. Calculate the
molar heat of combustion of phosphorus in kJ/mol.
6. A reference gives the molar enthalpy of combustion for methane as 803 kJ/mol. What
minimum mass of methane must be burned to warm 4.00 L of water from 22.4C to
87.6C, assuming no heat losses?
7. A 5.20 g sample of olive oil was burned in a calorimeter containing 150 mL of water.
The initial water temperature was 19.88C and the final temperature after combustion
was 29.10C. Calculate the enthalpy of combustion of olive oil.
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Jill Agnew