Physics (Part 1 - Part 3)

430 CHAPTER 12 | The Laws of Thermodynamics
■ CONCEPTUAL QUESTIONS
The conceptual questions in this chapter may be assigned online in Enhanced WebAssign.
1. What are some factors that affect the efficiency of automobile
engines?
2. If you shake a jar full of jelly beans of different sizes,
the larger beans tend to appear near the top and the
smaller ones tend to fall to the bottom. (a) Why does
that occur? (b) Does this process violate the second law
of thermodynamics?
3. Consider the human body performing a strenuous
exercise, such as lifting weights or riding a bicycle.
Work is being done by the body, and energy is leaving
by conduction from the skin into the surrounding
air. According to the first law of thermodynamics, the
temperature of the body should be steadily decreasing
during the exercise. That isn’t what happens, however.
Is the first law invalid for this situation? Explain.
4. Clearly distinguish among temperature, heat, and
internal energy.
5. For an ideal gas in an isothermal process, there is no
change in internal energy. Suppose the gas does work
W during such a process. How much energy is transferred
by heat?
6. A steam-driven turbine is one major component of an
electric power plant. Why is it advantageous to increase
the temperature of the steam as much as possible?
7. Is it possible to construct a heat engine that creates no
thermal pollution?
8. In solar ponds constructed in Israel, the Sun’s energy
is concentrated near the bottom of a salty pond. With
the proper layering of salt in the water, convection is
prevented and temperatures of 100°C may be reached.
Can you guess the maximum efficiency with which useful
mechanical work can be extracted from the pond?
9. When a sealed Thermos bottle full of hot coffee is
shaken, what changes, if any, take place in (a) the temperature
of the coffee and (b) its internal energy?
10. Give some examples of irreversible processes that occur
in nature. Give an example of a process in nature that
is nearly reversible.
11. The first law of thermodynamics says we can’t get more
out of a process than we put in, but the second law says
that we can’t break even. Explain this statement.
12. If a supersaturated sugar solution is allowed to evaporate
slowly, sugar crystals form in the container. Hence,
sugar molecules go from a disordered form (in solution)
to a highly ordered, crystalline form. Does this
process violate the second law of thermodynamics?
Explain.
13. Using the first law of thermodynamics, explain why the
total energy of an isolated system is always constant.
14. What is wrong with the following statement: “Given any
two bodies, the one with the higher temperature contains
more heat.”
■ PROBLEMS
The problems in this chapter may be assigned online in
Enhanced WebAssign. Selected problems also have Watch It video
solutions.
1. denotes straightforward problem; 2. denotes intermediate problem;
3. denotes challenging problem
1. denotes full solution available in Student Solutions Manual/
Study Guide
1. denotes problems most often assigned in Enhanced WebAssign
denotes biomedical problems
denotes guided problems
denotes Master It tutorial available in Enhanced WebAssign
denotes asking for quantitative and conceptual reasoning
denotes symbolic reasoning problem
12.1 Work in Thermodynamic Processes
1. An ideal gas is enclosed in a cylinder with a
movable piston on top of it. The piston has a mass of
8 000 g and an area of 5.00 cm 2 and is free to slide up
and down, keeping the pressure of the gas constant.
(a) How much work is done on the gas as the temperature
of 0.200 mol of the gas is raised from 20.0°C to
300°C? (b) What does the sign of your answer to part
(a) indicate?
2. Sketch a PV diagram and find the work done by the
gas during the following stages. (a) A gas is expanded
from a volume of 1.0 L to 3.0 L at a constant pressure of
3.0 atm. (b) The gas is then cooled at constant volume
until the pressure falls to 2.0 atm. (c) The gas is then
compressed at a constant pressure of 2.0 atm from
a volume of 3.0 L to 1.0 L. Note: Be careful of signs.
(d) The gas is heated until its pressure increases from
2.0 atm to 3.0 atm at a constant volume. (e) Find the
net work done during the complete cycle.
3. Gas in a container is at a pressure of 1.5 atm and
a volume of 4.0 m 3 . What is the work done on the gas
(a) if it expands at constant pressure to twice its initial
volume, and (b) if it is compressed at constant pressure
to one-quarter its initial volume?
Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.