SCH 4UK
Energy Unit Assignment
Calorimetry Problems
In the following 5 questions, if there is a bomb calorimeter being used, assume that all heat is absorbed by the water, i.e.
that the heat absorbed by the 'bomb' itself is insignificant. Exception is #6
1. When 1.37 g of barium reacts with oxygen, there is a release of 5.57 x 103 J of energy. How much heat would be
produced during the formation of 1.00 mol of barium oxide. (Answer 558 kJ is produced)
2. The heat produced by burning 1.00 g of hydrazine (N2H4) is collected in 3.95 kg of water in a calorimeter. If the
temperature rise is 1.2 K, calculate the molar heat of combustion of hydrazine. (Answer -6.3 x 102 kJ/mol)
3. Octane, (C8H18), is one component of gasoline. The heat produced by burning 1.00 g of octane is collected in 2.00 kg
of water in a calorimeter. The temperature rise was 24.4 K. Calculate the molar heat of combustion of octane.
(Answer -2.33 x 104 kJ/mol)
4. A particular calorimeter contains 3.54 kg of water. When 8.36 g of calcium are made to react with excess chlorine gas
in this calorimeter, the observed temperature rise is 11.2 K. Calculate the molar heat of formation of calcium chloride.
(Answer - 7.94 x 102 kJ/mol)
5. A bomb calorimeter contains 1.68 kg of water surrounding the bomb. Chlorine gas was pumped into the bomb until
the pressure was 1.21 x 103 kPa at 27.0°C. Then an excess of hydrogen gas was pumped into the calorimeter and the
mixture was ignited. The observed temperature rise was 28.5 K. If all of the heat was collected in the water and the
volume of the bomb was 2.24 L. Calculate the molar heat of formation of hydrogen chloride gas.
(Answer -92.1 kJ/mol)
6. A calorimeter consists of an aluminum bomb with a mass of 1.080 kg immersed in 970.0 g of water, all contained in a
well-insulated system at an initial temperature of 24.92C. A 0.486 g sample of pure magnesium ribbon is added to
the bomb. The bomb is then filled with pure oxygen gas and sealed. A surge of electrical energy is sent through the
magnesium ribbon, causing it to ignite. After the magnesium has all burned and the heat was transferred through the
walls of the bomb, the final temperature is 27.30°C. The specific heat capacity of aluminum is 9.05 x 102 J/kg.K.
Calculate the molar heat of formation of magnesium oxide from these data.
(Answer -599 kJ/mol)
4.1
3.00 g of potassium hydroxide (KOH) pellets are put into a Styrofoam calorimeter (i.e. a used Styrofoam coffee
cup) containing 250 mL of water. The initial temperature of the water is 22.3°C. The mixture is then stirred until all of the
KOH is dissolved. The final temperature of the solution is measured and recorded as 29. 7 C. Calculate the heat of
solution for potassium hydroxide (ΔHsol’n) . The specific heat capacity of the solution may be assumed to be the same as
that of water since this is a dilute solution (3 g in 250 mL is roughly a 1 % solution). Assume no heat loss from the
calorimeter. Ignore the mass of solute when calculating q. (ΔHsol’n = -144 kJ/mol)
4.2
12.72 g of ammonium chloride is dissolved in 100 mL of water in an insulated calorimeter so that the temperature
changes from 24.7C to 7. 2C. Calculate the heat of solution of ammonium chloride assuming that the specific heat
capacity of the solution is the same as that of water. Ignore the mass of solute when calculating q. (ΔHsol’n= 30.7kJ/mol)
4.3
A sample of sucrose (C12H22O11) with a mass of 1.32 g is burned in a bomb calorimeter. The overall heat capacity
(C x m) of the calorimeter has been previously determined to be 9.43 kJ C-1. The temperature of the calorimeter changed
from 25.00°C to 27.31 C. Calculate the heat of combustion of sucrose. (ΔHcomb.= -5.64 x 103kJ/mol)
4.4
A sample of carbon with a mass of 4.00 g is burned in a 500 g "bomb " calorimeter made of nickel metal [CNi =
0.444 kJ/(kg.C)]. The bomb calorimeter is immersed in an insulated container containing 1.50 kg of water. The
temperature is measured before and after and found to increase from 22.75°C to 42.98°C. Calculate the molar heat of
combustion of carbon. (ΔH= -394 kJ/mol)
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SCH 4UK
Energy Unit Assignment
5.1
Rewrite each of the equations below as a thermochemical equation. ∆Hrx is the molar enthalpy of reaction.
5.1.1 NO(g)  ½N2(g) + ½ O2(g)
Hrx = -90.4 kJ
5.1.2 CO2(g) +3/2 H2O(g)
1/2 C2H6(g) + 7/4 O2(g)
Hrx = +714.1 kJ
5.1.3 NH3(g) + 7/4 O2(g) NO 2(g) + 3/2 H2O(g)
Hrx = -283.0 kJ
For each of the equations below express the heat of reaction in Hrx notation per mole of the bolded quantity.
Classify each reaction as exothermic or endothermic.
Example.
Ca(s) + ½ O2(g) → CaO(s) + 636 kJ
rx is exothermic
Answer: Hrx = -636 kJ / ½ mol O2 = -1272 kJ/mol O2
= -1.27 x 103 kJ/mol O2
5.2
5.2.1
½ N2(g) + O2 (g) + 33.9 kJ→NO2(g)
Hrn = 33.9 kJ/mol NO2
5.2.2
½ N2(g) +
Hrn = -30.8 kJ/mol H2
5.2.3
C3H8(g) → 3 C(s) + 4 H2(g) + 104kJ
5.3
A given mass of ammonium chloride dissolves in 50.0 mL of water causing a temperature change from 23.0°C to
14.7°C. Is the solubility of ammonium chloride exo- or endothermic?
5.4
2.50 g of sodium hydroxide dissolves in 100 mL of water causing a temperature change from 21.6°C to 27.4°C.
Classify the solubility of sodium hydroxide as exothermic or endothermic.
5.5
Are combustion reactions in general exothermic or endothermic? Explain.
5.6
Write thermochemical equations for the combustion of one mole of each of the given compounds. Assume that
the products are "the usual" gaseous products for burning hydrocarbons, at standard conditions. The standard
heats of combustion (∆Hcomb) are given in brackets.
3
2
H2 → NH3 + 46.2 kJ
Question no.
5.6.1
5.6.2
5.6.3
5.6.4
Hrn = -26 kJ/mol H2
compound
acetylene, C2H2(g)
methyl alcohol, CH3OH(l)
ethoxyethane, C4H10O(l)
toluene, C7H8(l)
∆Hcomb
(-1299.6 kJ/mol)
(- 726.51 kJ/mol)
(-2751.1 kJ/mol)
(-3909 kJ/mol)
7.1
What is the connection between Hess' Law and the fact that H is a state function?
7.2
Consider the following hypothetical reactions:
A→B
H = + 30 kJ
B→C
H = + 60 kJ
Use Hess' Law to calculate the enthalpy change for the reaction A → C
7.3
Suppose you have the following hypothetical reactions:
X→Y
H = -50kJ
X→ Z
H = -70 kJ
Use Hess' Law to calculate the enthalpy change for the reaction Y → Z
7.4 Use the METHOD OF SUMMING EQUATIONS to calculate the heat of reaction (enthalpy change) for each of the
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SCH 4UK
Energy Unit Assignment
reactions represented by the equations below:
7.4.1 C2H6(g) + 7/2 O2(g) →2 CO2(g) + 3 H2O(l)
7.4.2 C6H6(g) + 6 H2(g) →3 C2H6(g)
7.4.3 C3H8(g) + 5 O2(g) →3 CO2(g) + 4 H2O(l)
7.4.4 H2O(g) + C(s) →CO(g) + H2(g)
7.5
Calculate the entha1py change for the reaction P4(s) + 10 Cl2(g)
corresponding enthalpy changes:
P 4(s) + 6 Cl2(g) →4 PCl3 (1)
PCl3(1) + Cl2(g) →PCl5(s)
4 PC15(s) given the following equations and
H = -1272.5 kJ
H = -137.3 kJ
7.6
Calculate the heat of formation of methanol, CH3OH(l), given the following:
CH3OH(l) + 3 2 O2(g) →CO2(g) + 2 H2O(l)
H = -728.7 kJ
C(s) + O2(g) →CO2(g)
H= -393.7 kJ
H2(g) + ½ O2(g) →H2O(l)
H = -285.9 kJ
8.
Use the formula method to calculate the heat of reaction for each of the following equations.
(i.e. Hrn = Hf products - Hf reactants.)
8.1
2C6H6(g) + 15 O2(g) →12 CO2(g) + 6H2O(l)
8.2
C6H6(g) + 6 H2 → 3 C2H6(g)
8.3
C3H8(g) + 5O2(g) →3 CO2(g) + 4 H2O(l)
8.4
H2O(l) + C(s) →CO(g) + H2(g)
8.5
8.6
Calculate the heat of combustion of methane assuming that the products are gaseous.
Calculate the heat of combustion of propane, C3H8, assuming that the products are gaseous.
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
b. propane C3H8
c. oxalic acid, H2C2O4
ΔH of combustion
1410 kJ/mol
2220 kJ/mol
252 kJ/mol
answer ΔHf
50.8 kJ/mol
104.7 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 are carbon dioxide and liquid water.
compound
a. ethane,C2H6(g)
b. acetylene, C2H2(g)
c. benzoic acid,
C7H6O2(s)
ΔHf
84.6 kJ/mol
+227 kJ/mol
390 kJ/mol
answer ΔHcomb.
1560.5 kJ/mol
1300 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. Why are these values only similar, not the same?
(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
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SCH 4UK
Energy Unit Assignment
combustion of ethanol is -1371 kJ/mol what will be the temperature of the calorimeter when combustion is complete?
(Answer 32.3°C)
ADDITIONAL VALUES NEEDED FOR THESE 8 QUESTIONS:
Hf C2H6(g) = - 84.4 kJ/mol
Hf C2H2(g) = + 222.8 kJ/mol
Hf 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)
H = + 1660 kJ
O2(g)2O(g)
H= + 490kJ
2 H(g) + O(g)H20(g)
H = - 930 kJ
C(g) + 2 O(g)CO2(g)
H = - 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.
(Answer -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)
Hrn = - 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(l)
(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. (answer 1.63 x 103kJ)
SO3(g) + H2O(l)  H2SO4(l)
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)
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