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General Chemistry
Principles & Modern Applications
9th Edition
Petrucci/Harwood/Herring/Madura
Chapter 7
Thermochemistry
Dr. Travis D. Fridgen
Memorial University of Newfoundland
© 2007 Pearson Education
When heat is absorbed by ice (the system)
it melts. The quantity q for the system is
1. positive.
2. negative.
3. 0
When heat is absorbed by ice (the system)
it melts. The quantity q for the system is
1. positive.
2. negative.
3. 0
When potassium chlorate decomposes
it produces oxygen gas. From the
system’s point of view (which is the
convention), w is
1. positive.
2. negative.
3. No work done.
When potassium chlorate decomposes
it produces oxygen gas. From the
system’s point of view (which is the
convention), w is
1. positive.
2. negative.
3. No work done.
Heat is added to the container below while being allowed to expand freely
against atmospheric pressure. The temperature and pressure, however,
remain constant before and after.
DU is,
1. positive.
2. negative.
3. 0
Heat is added to the container below while being allowed to expand freely
against atmospheric pressure. The temperature and pressure, however,
remain constant before and after.
DU is,
1. positive.
2. negative.
3. 0
The volume of the Atlantic Ocean is about 300 km3. Without the use of a
calculator, estimate the heat that is required to raise the temperature of the
Atlantic Ocean by 1 oC (assume the density of water is 1 g cm-3 and the
specific heat is 4 J g-1 oC-1.
1. ~103 J
2. ~106 J
3. ~1012 J
4. ~1018 J
5. ~1025 J
The volume of the Atlantic Ocean is about 300 km3. Without the use of a
calculator, estimate the heat that is required to raise the temperature of the
Atlantic Ocean by 1 oC (assume the density of water is 1 g cm-3 and the
specific heat is 4 J g-1 oC-1.
1. ~103 J
2. ~106 J
3. ~1012 J
4. ~1018 J
5. ~1025 J
In 1 minute the sun shines about 40 kJ m-2 of energy on Earth’s surface and
about 1018 J is required to raise the temperature of the Atlantic by 1 oC.
Assuming that all of the sun’s energy is absorbed, how long must the sun shine
on the Atlantic to raise its temperature
by 1 oC? The area of the Atlantic ocean
is about 100 km2.
1. 4x1021 min
2. 2.5x1011 min
3. 2.5x105 min
4. 2.5x10-5 min
5. 4x10-10 min
Where does the energy come from to heat the ocean?
In 1 minute the sun shines about 40 kJ m-2 of energy on Earth’s surface and
about 1018 J is required to raise the temperature of the Atlantic by 1 oC.
Assuming that all of the sun’s energy is absorbed, how long must the sun shine
on the Atlantic to raise its temperature
by 1 oC? The area of the Atlantic ocean
is about 100 km2.
1. 4x1021 min
2. 2.5x1011 min
3. 2.5x105 min
4. 2.5x10-5 min
5. 4x10-10 min
Where does the energy come from to heat the ocean?
You take two frozen steaks and put them into room temperature water for a few
hours to thaw. The heat gained by the steak (system) equals the heat lost by
the water (surroundings). The best equation to express this, where subscript ‘s’
refers to steak and the subscript w refers to the water, is,
1. sw mw DTw = ss ms DTs
2. sw mw DTw =  ss ms DTs
3.  sw mw DTw = ss ms DTs
You take two frozen steaks and put them into room temperature water for a few
hours to thaw. The heat gained by the steak (system) equals the heat lost by
the water (surroundings). The best equation to express this, where subscript ‘s’
refers to steak and the subscript w refers to the water, is,
1. sw mw DTw = ss ms DTs
2. sw mw DTw =  ss ms DTs
3.  sw mw DTw = ss ms DTs
What is the heat capacity of
Tellurium? Use 4 J g-1 oC-1
for the heat capacity of
water.
qTe = qH2O
1. 0.5 J g-1 oC-1
2. 1 J g-1 oC-1
3. 2 J g-1 oC-1
4. 4 J g-1 oC-1
5. 10 J g-1 oC-1
200 g Te
(100 oC)
100 g H2O
25 oC
50 oC
What is the heat capacity of
Tellurium? Use 4 J g-1 oC-1
for the heat capacity of
water.
qTe = qH2O
1. 0.5 J g-1 oC-1
2. 1 J g-1 oC-1
3. 2 J g-1 oC-1
4. 4 J g-1 oC-1
5. 10 J g-1 oC-1
200 g Te
(100 oC)
100 g H2O
25 oC
50 oC
Determine DH and DU for the reaction and conditions depicted below.
Note: 1 Pa = 1 N m-2.
DH
DU
1. 250 kJ,
251 kJ
2. 250 kJ,
249 kJ
3. -250 kJ,
-251 kJ
4. -250 kJ,
-249 kJ
5. -250 kJ,
-250 kJ
V1= 0.120 m3
V2= 0.110 m3
1x105 Pa
qP = 250 kJ
T=300 K
Determine DH and DU for the reaction and conditions depicted below.
Note: 1 Pa = 1 N m-2.
DH
DU
1. 250 kJ,
251 kJ
2. 250 kJ,
249 kJ
3. -250 kJ,
-251 kJ
4. -250 kJ,
-249 kJ
5. -250 kJ,
-250 kJ
V1= 0.120 m3
V2= 0.110 m3
1x105 Pa
qP = 250 kJ
T=300 K
Ice (the system) melting is
1. an exothermic process.
2. an endothermic process.
3. neither exothermic nor endothermic since the temperature
of the system remains constant (0 oC at 1 atm).
Note: a bit tricky perhaps until chapter 13.
Ice (the system) melting is
1. an exothermic process.
2. an endothermic process.
3. neither exothermic nor endothermic since the temperature
of the system remains constant (0 oC at 1 atm).
Note: a bit tricky perhaps until chapter 13.
The equation for the combustion of butane is,
C4 H10 (g) +
13
O 2 (g)  4CO 2 (g) + 5H 2O(g)
2
Which one of the following generates the least heat?
1. Burning one mole of butane in excess oxygen.
2. Reacting one mole of oxygen with excess butane.
3. Producing one mole of carbon dioxide by burning butane.
4. Producing one mole of water by burning butane.
5. Burning 0.25 moles of butane with excess oxygen.
The equation for the combustion of butane is,
C4 H10 (g) +
13
O 2 (g)  4CO 2 (g) + 5H 2O(g)
2
Which one of the following generates the least heat?
1. Burning one mole of butane in excess oxygen.
2. Reacting one mole of oxygen with excess butane.
3. Producing one mole of carbon dioxide by burning butane.
4. Producing one mole of water by burning butane.
5. Burning 0.25 moles of butane with excess oxygen.
The chemical reaction representing aerobic respiration is,
C6H12O6 (s) + 6O2 (g)  6CO2 (g) + 6H2O(g)
and is the reverse of photosynthesis. This reaction is exothermic by ~2500 kJ per
mole of glucose. A small child exhales about 3 moles of CO2 in a 24 hour period,
what is the energy change associated with the photosynthesis reaction required to
convert this amount of CO2 back to glucose?
1. 5000 kJ
2. -5000 kJ
3. -2500 kJ
4. 1250 kJ
5. -1250 kJ
The chemical reaction representing aerobic respiration is,
C6H12O6 (s) + 6O2 (g)  6CO2 (g) + 6H2O(g)
and is the reverse of photosynthesis. This reaction is exothermic by ~2500 kJ per
mole of glucose. A small child exhales about 3 moles of CO2 in a 24 hour period,
what is the energy change associated with the photosynthesis reaction required to
convert this amount of CO2 back to glucose?
1. 5000 kJ
2. -5000 kJ
3. -2500 kJ
4. 1250 kJ
5. -1250 kJ
Given the heats of formation of the potential products of the Ostwald process,
which reaction is most exothermic?
1. NH 3 (g) +
3
O 2 (g)
4
2. NH 3 (g) + O2 (g)


DH / kJ
mol-1
1
3
N 2 (g) + H 2O(g)
2
2
1
3
N 2O(g) + H 2O(g)
2
2
3. NH 3 (g) +
5
O2 (g)
4

4. NH 3 (g) +
7
O2 (g)
4
 NO 2 (g) +
NO(g) +
3
H 2O(g)
2
3
H 2O(g)
2
N2
0
N2O
82.1
NO
90.2
NO2
33.2
Given the heats of formation of the potential products of the Ostwald process,
which reaction is most exothermic?
1. NH 3 (g) +
3
O2 (g) 
4
2. NH 3 (g) + O2 (g)

DH / kJ
mol-1
1
3
N 2 (g) + H 2O(g)
2
2
1
3
N 2O(g) + H 2O(g)
2
2
3. NH 3 (g) +
5
O2 (g)
4

4. NH 3 (g) +
7
O2 (g)
4
 NO 2 (g) +
NO(g) +
3
H 2O(g)
2
3
H 2O(g)
2
N2
0
N2O
82.1
NO
90.2
NO2
33.2
Given the heats of formation of the potential products of the Ostwald process,
which reaction is most exothermic?
DH / kJ
mol-1
1. 4NH3 (g) + 3O2 (g)  2N2 (g) + 6H2O(g)
N2
0
N2O
82.1
3. 4NH3 (g) + 5O2 (g)  4NO(g) + 6H2O(g)
NO
90.2
4. 4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H 2O(g)
NO2
33.2
2. 2NH3 (g) + 2O2 (g)  N2O(g) + 3H2O(g)
Given the heats of formation of the potential products of the Ostwald process,
which reaction is most exothermic?
DH / kJ
mol-1
1. 4NH3 (g) + 3O2 (g)  2N2 (g) + 6H2O(g)
N2
0
N2O
82.1
3. 4NH3 (g) + 5O2 (g)  4NO(g) + 6H 2O(g)
NO
90.2
4. 4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H 2O(g)
NO2
33.2
2. 2NH3 (g) + 2O2 (g)  N2O(g) + 3H2O(g)
The equations for the complete and incomplete combustion of octane are given
below.
DHf / kJ
25
C8 H18 (l) +
O2 (g)  8CO 2 (g) + 9H 2O(l)
mol-1
2
C8 H18 (l) +
17
O2 (g)  8CO(g) + 9H 2O(l)
2
CO
-111
CO2
-394
Which reaction is more exothermic and by
how much?
1. Incomplete by 283 kJ mol-1.
2. Incomplete by 2264 kJ mol-1.
3. Complete by 2264 kJ mol-1.
4. Complete by 283 kJ mol-1.
5. Complete by 505 kJ mol-1.
The equations for the complete and incomplete combustion of octane are given
below.
DHf / kJ
25
C8 H18 (l) +
O2 (g)  8CO 2 (g) + 9H 2O(l)
mol-1
2
C8 H18 (l) +
17
O2 (g)  8CO(g) + 9H 2O(l)
2
CO
-111
CO2
-394
Which reaction is more exothermic and by
how much?
1. Incomplete by 283 kJ mol-1.
2. Incomplete by 2264 kJ mol-1.
3. Complete by 2264 kJ mol-1.
4. Complete by 283 kJ mol-1.
5. Complete by 505 kJ mol-1.
Two equations incomplete combustion of butane are given below.
9
A. C4 H10 (g) + O 2 (g)  4CO(g) + 5H 2O(l)
2
B. C4 H10 (g) +
5
O2 (g)  8C(graph) + 5H 2O(l)
2
DHf = -111 kJ mol-1
Given that the heat of formation of CO(g) is -111 kJ mol-1, which reaction is
more exothermic and by how much?
1. Reaction A by 111 kJ mol-1.
4. Reaction B by 444 kJ mol-1.
2. Reaction B by 111 kJ mol-1.
5. Not enough information to answer.
3. Reaction A by 444 kJ
mol-1.
Two equations incomplete combustion of butane are given below.
9
A. C4 H10 (g) + O 2 (g)  4CO(g) + 5H 2O(l)
2
B. C4 H10 (g) +
5
O2 (g)  8C(graph) + 5H 2O(l)
2
DHf = -111 kJ mol-1
Given that the heat of formation of CO(g) is -111 kJ mol-1, which reaction is
more exothermic and by how much?
1. Reaction A by 111 kJ mol-1.
4. Reaction B by 444 kJ mol-1.
2. Reaction B by 111 kJ mol-1.
5. Not enough information to answer.
3. Reaction A by 444 kJ
mol-1.
Given the bond energies below, estimate the enthalpy change for the
addition of Br across the double bond in ethene.
+
1. 150 kJ
2. -150 kJ
3. 220 kJ
4. -220 kJ
5. Not enough data to determine DrH
C—C
C=C
C—Br
Br—Br
350 kJ mol-1
600 kJ mol-1
300 kJ mol-1
200 kJ mol-1
Given the bond energies below, estimate the enthalpy change for the
addition of Br across the double bond in ethene.
+
1. 150 kJ
2. -150 kJ
3. 220 kJ
4. -220 kJ
5. Not enough data to determine DrH
C—C
C=C
C—Br
Br—Br
350 kJ mol-1
600 kJ mol-1
300 kJ mol-1
200 kJ mol-1