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Student Worksheet Solutions
LSM 11.5G
Solutions for Multi-Step Energy Calculations,
Extra Exercises
1. For the following combustion reaction, what mass of carbon dioxide is produced when 1500
kJ of energy is released?
2 C2H6(g) + 7 O2(g) o4 CO2(g) + 6 H2O(g) + 2502 kJ
ǻ H -2502 kJ
ǻc H mol = c =
= -626 kJ/mol CO 2
n
4 mol
ǻc H = nǻc H mol
1 mol
× 626 kJ/mol
44.01 g
m = 105 g
According to the evidence given, 106 g carbon dioxide will be produced for every
1500 kJ of energy released.
1500 kJ = m ×
2. How much energy is released when 1.00 t of sulfur trioxide is produced by the following
reaction?
2 SO2(g) + O2(g) o 2 SO3(g)
'rH = –192.8 kJ
ǻ H -192.8 kJ
ǻr H mol = r =
= -96.4 kJ/mol SO 3
n
2 mol
ǻr H = nǻr H mol
1 mol 96.4 kJ
×
= 1.20 GJ
80.06 g 1 mol
According to the evidence given, 1.20 GJ of energy is released when 1.00 t of sulfur
trioxide is produced.
= 1.00 Mg ×
3. 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?
C6H12O6(s) + 6 O2(g) o 6 CO2(g) + 6 H2O(l)
ǻr H ° =
nǻfP H ° - nǻfR H °
¦
¦
-393.5 kJ
-285.8 kJ · §
-1273.3 kJ
-0 kJ ·
§
= ¨ 6 mol ×
+ 6 mol ×
- ¨ 1 mol ×
+ 6 mol ×
¸
¸
©
1 mol
1 mol ¹ ©
1 mol
1 mol ¹
= -4075.8 kJ - -1273.3 kJ = -2802.5 kJ
-2802.5 kJ
= 2802.5 kJ/mol C6 H12O6
1 mol
ǻc H = nǻc H mol
1 mol
-2802.5 kJ
= 18.0 g ×
×
180.18.g
1 mol
= -280 kJ
According to referenced information, 280 kJ of energy is released when 18.0 g of
glucose is consumed.
ǻc H mol =
400
Unit 6 Lab and Study Masters
Copyright © 2007 Thomson Nelson
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LSM 11.5G (cont’d)
4. Methanol is burned in a bomb calorimeter. Liquid water is formed as a product. If 3.40 g of
methanol reacts, what is the expected temperature change in a 6.00 kg calorimeter with a heat
capacity of 1.125 J/(g•°C)?
CH3OH(l) + 3 O2(g) o CO2(g) + 2 H2O(l)
2
ǻr H ° =
¦ nǻfP H ° - ¦ nǻfR H °
-393.5 kJ
-285.8 kJ · §
-277.6 kJ 3
0 kJ ·
§
= ¨ 1 mol ×
+ 2 mol ×
- ¨ 1 mol ×
+ mol ×
¸
¸
©
1 mol
1 mol ¹ ©
1 mol
2
1 mol ¹
= -965.1 kJ - -277.6 kJ = -687.5 kJ
ǻc H mol =
-687.5 kJ
= -687.5 kJ/mol CH 3OH
1 mol
ǻc H = mcǻt
(methanol)
3.40 g ×
(calorimeter)
1 mol -687.5 kJ
J
×
= 1.00 kg ×1.125
× ǻt
32.05 g
1 mol
g • oC
ǻt = 10.8 o C
According to referenced information and the evidence provided, the temperature of the
calorimeter will change by 10.8 qC is released when 3.40 g of methanol is burned.
5. A waste heat exchanger is used to absorb the energy from the complete combustion of
hydrogen sulfide gas. What volume of water undergoing a temperature change of 64 °C is
required to absorb all of the energy from the burning of 15 kg of hydrogen sulfide?
H2S(g) + 3 O2(g) o SO2(g) + H2O(g)
2
ǻr H ° =
¦ nǻfP H ° - ¦ nǻfR H °
-296.8 kJ
-241.8 kJ · §
-20.6 kJ 3
0 kJ ·
§
= ¨ 1 mol ×
+ 1 mol ×
- ¨ 1 mol ×
+ mol ×
¸
¸
©
1 mol
1 mol ¹ ©
1 mol
2
1 mol ¹
= -538.6 kJ - -20.6 kJ = -508.0 kJ
ǻc H mol =
-508.0 kJ
= -508.0 kJ/mol H 2S
1 mol
ǻc H = Q
(H 2S)
(water)
nǻc H mol = mcǻt
15 kg ×
1 mol -508.0 kJ
4.19 J
×
= m×
× 64 o C
o
34.09 g
1 mol
g• C
m = 834 kg
V = 8.3 ×102 L
According to referenced information and the evidence provided, 8.3 u 102 L of water
will warm by 64 qC when 15 kg of hydrogen sulfide is burned.
Copyright © 2007 Thomson Nelson
Unit 6 Lab and Study Masters
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