SCH 4UK
Enthalpy Worksheet #1
ADDITIONAL VALUES NEEDED ON THIS SHEET: DHf° C2H6(g) = - 84.4 kJ/mol
DHf° C2H2(g) = + 222.8 kJ/mol DHf° C3H8(g) = - 103.7 kJ/mol
1. Octane, C8H18, is one component of gasoline. The heat produced by burning 1.00 g of octane is
collected in 2.95 kg of water in a calorimeter. If the temperature rise is 16.24 K, calculate the
molar heat of combustion of octane.(Answer -2.28 x 104 kJ/mol)
2. Using the following equations and their associated enthalpy changes calculate the molar heat of
combustion of methane gas (CH4). (Answer -830 kJ/mol)
CH4(g)C(g) + 4 H(g)
D H = + 1660 kJ
O2(g)2O(g)
DH= + 490kJ
2 H(g) + O(g)H20(g)
D H = - 930 kJ
C(g) + 2 O(g)CO2(g) DH = - 1610 kJ
3. Using standard enthalpies of formation, calculate the heat of combustion per mole of gaseous
water formed during the complete combustion of ethane gas (C2H6).
(Answer -476.2 kJ/mol H2O(g)
4. a) Using standard enthalpies of formation, calculate the heat of hydrogenation of acetylene gas,
C2H2(g) , to form ethane gas.
C2H2 + 2H2  C2H6(g) (Answer-307.4 kJ)
b) Calculate the heat of hydrogenation of acetylene(C2H2) using bond energies. (Ans. -321 kJ)
5. Using the following information, calculate the standard enthalpy of formation of solid calcium
carbide. (Answer -62.6 kJ/mol)
CaC2(s) + 2 H2O(1)  Ca(OH)2(s) + C2H2(g)
DHrn° = - 129.9 kJ/mol CaC2(s)
6. When 1.520 g of carbon disulfide is burned according to the equation
CS2(l) + 3 O2(g)  CO2(g) + 2 SO2(g)
21.54 kJ of heat were released. Calculate the standard enthalpy of formation of CS2.
(Answer 91.9 kJ/mol)
7. If the standard enthalpy of formation of H2SO4(l) is -812.2 kJ/mol, calculate the amount of
energy released when 1000 g of sulfur trioxide reacts according to the equation
SO3(g) + H2O(l)  H2SO4(l) (Answer 1636 kJ)
8. The heat of combustion of propane gas is measured in a copper bomb calorimeter. The copper
bomb has a mass of 12.7 kg and is immersed in 1.20 kg of water. The specific heat capacity of
copper is 0.386 kJkg-1K-1 What temperature change in the copper bomb plus water would be
noted if 1.00 x 10-2 mol of propane gas are completely burned in pure oxygen in this calorimeter
to produce carbon dioxide gas and liquid water?
(Answer 2.24 K)
SCH 4UK
Enthalpy Worksheet #1
1. From the following values of heats of combustion of organic molecules, calculate their heats of
formation. The products in each combustion are carbon dioxide and liquid water.
compound
a. ethene, C2H4
Δ Hcomb
1410 kJ/mol
ΔHf
50.8 kJ/mol
b. propane C3H8
2220 kJ/mol
104.7 kJ/mol)
c. oxalic acid,
H2C2O4
252 kJ/mol
821.3 kJ/mol)
2. Given the following heats of formation, calculate the heat of combustion of each of the following
compounds. The products in each combustion reaction are carbon dioxide and liquid water.
compound
ΔHf
ΔHcomb
a. ethane,
C2H6(g) 84.6 kJ/mol
1560.5 kJ/mol
b. acetylene, C2H2(g)
1300 kJ/mol)
+227 kJ/mol
c. benzoic acid,
C7H6O2(s)
390 kJ/mol
3223.6 kJ/mol
3. Ammonia gas (NH3) reacts with oxygen gas to produce nitrogen gas and water vapour. Calculate
the heat of reaction using: a. bond energies and b. heats of formation.
(Answers a. -324 kJ/mol ammonia b. -316.8 kJ/mol ammonia)
4. A calorimeter with a mass of 1.63 kg and a specific heat capacity of 897.5 J/kg.K contains 880 g
of water. 3.00 g of acetic acid, CH3COOH(l), which is burned in an excess of oxygen gas in the
calorimeter to give carbon dioxide and liquid water. The temperature was observed to rise from
20.1°C to 28.6°C. Calculate the molar heat of combustion of acetic acid.
(Answer -874 kJ/mol)
5. A calorimeter with a mass of 1.49 kg and a specific heat capacity of 897.5 J/kg.K contains 718 g
of water. Initially the apparatus is at 22.0°C and contains 1.50 g of ethanol (CH3CH2OH) mixed
with excess oxygen. If the heat of combustion of ethanol is -1371 kJ/mol what will be the
temperature of the calorimeter when combustion is complete? (Answer 32.3°C)