Section 3

Name:______________________________Class:__________________ Date:__________________
Assessment
Thermodynamics
Teacher Notes and Answers
10 Thermodynamics
THE SECOND LAW OF THERMODYNAMICS
1.
2.
3.
4.
b
a
d
d
Given
8. a
9. According to the second law of
thermodynamics, energy (Qc) must be given
up as heat to a lower-temperature body from
a heat engine. Because Qc is always greater
than zero, the ratio of energy transferred
from the engine as heat to the energy
transferred to the engine as heat (Qc/Qh) is
greater than zero. For an engine to be 100
percent efficient, this ratio must be zero.
Therefore, the second law of
thermodynamics predicts that no heat engine
can be 100 percent efficient.
10. 0.25
Given
Qh = 7.6 105 J
Qc = 5.7 105 J
Solution
Q
eff = 1 c
Qh
2
Qc = Qh
3
Solution
2
Qh
Qc
2 1
eff = 1
= 1 3
= 1 =
3 3
Qh
Qh
5. c
Given
Qh = 2.5 104 J
Wnet = 7.0 103 J
Solution
W
7.0 103 J
eff = net =
= 0.28
Qh
2.5 10 4 J
6. b
7. a
5
eff = 1
5.710 J
5
7.610 J
= 1 0.75 = 0.25
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
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Section Quizzes
Name:______________________________Class:__________________ Date:__________________
Assessment
Thermodynamics
Section Quiz: The Second Law of Thermodynamics
Write the letter of the correct answer in the space provided.
_____ 1. Which of the following statements results from the second law of
thermodynamics?
a. Energy added to a system as heat is entirely converted to work.
b. Energy added to a system as heat cannot be converted entirely to
work.
c. Energy added to a system as heat equals the increase in entropy.
d. Energy added to a system as heat equals the heat given up to the
surroundings.
_____ 2. Which of the following situations would cause an ideal heat engine to
do more work and still perform a cyclic process?
a. increase the heat from the high-temperature reservoir
b. decrease the heat from the high-temperature reservoir
c. increase the heat removed to the low-temperature reservoir
d. prevent any heat from being removed to the low-temperature
reservoir
_____ 3. A power plant transfers 82 percent of the energy produced from
burning fuel to convert water to steam. Of the energy transferred as
heat by the steam, 36 percent is converted doing work through a
spinning turbine. Which equation best describes the overall efficiency
of the heat-to-work conversion in the plant?
a. eff > 82 percent
b. eff = 82 percent
c. eff = 36 percent
d. eff < 36 percent
_____ 4. If two-thirds of the energy added to an engine as heat is removed to the
engine’s surroundings as heat, what is the efficiency of the engine?
a. 1
b. 2/3
c. 1/2
d. 1/3
_____ 5. If the energy added to an engine as heat is 2.5 104 J and the net work
done by the engine is 7.0 103 J what is the engine’s efficiency?
a. 0.72
b. 0.39
c. 0.28
d. 0.22
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
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Section Quizzes
Name:______________________________Class:__________________ Date:__________________
Thermodynamics continued
_____ 6. Work was done to freeze 1 kg of water. Which statement best describes
what happened to this system?
a. Its entropy increased.
b. Its entropy remained constant.
c. Its entropy decreased.
d. Freezing occurred spontaneously.
_____ 7. What must be true of the combined entropy of a system and its
environment?
a. It increases.
b. It remains constant.
c. It decreases.
d. It decreases at first, then increases.
_____ 8. If the entropy of a system decreases during a thermodynamic process,
what must be true about the change in the entropy of the environment?
a. It increases.
b. It remains constant.
c. It decreases.
d. It decreases at first, then increases.
9. Use the second law of thermodynamics to explain why a heat engine cannot be
100 percent efficient.
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10. An engine takes in 7.6 105 J of energy as heat and gives up 5.7 105 J of
energy as heat to the surroundings. What is the efficiency of the engine?
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
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Section Quizzes