UniversityPhysicsVolume2-Ch03. Old Dominion University PHYS 232N

University Physics Volume II
Unit 1: Thermodynamics
Chapter 3: The First Law of Thermodynamics
Conceptual Questions
1. Consider these scenarios and state whether work is done by the system on the environment
(SE) or by the environment on the system (ES): (a) opening a carbonated beverage; (b) filling a
flat tire; (c) a sealed empty gas can expands on a hot day, bowing out the walls.
Solution
a. SE; b. ES; c. ES
2. Is it possible to determine whether a change in internal energy is caused by heat transferred, by
work performed, or by a combination of the two?
Solution
Unless the situation is given, you cannot determine whether a change in internal energy is caused
by heat transfer, work, or a combination of the two.
3. When a liquid is vaporized, its change in internal energy is not equal to the heat added. Why?
Solution
Some of the energy goes into changing the phase of the liquid to gas.
4. Why does a bicycle pump feel warm as you inflate your tire?
Solution
As you pump a tire, you transfer energy to the air inside the pump. As that air moves into a
smaller volume, the air molecules collide more with the walls of the pump. Therefore, the pump
feels hotter.
5. Is it possible for the temperature of a system to remain constant when heat flows into or out of
it? If so, give examples.
Solution
Yes, as long as the work done equals the heat added there will be no change in internal energy
and thereby no change in temperature. When water freezes or when ice melts while removing or
adding heat, respectively, the temperature remains constant.
6. What does the first law of thermodynamics tell us about the energy of the universe?
Solution
You cannot get more energy out of a system than you put in.
7. Does adding heat to a system always increase its internal energy?
Solution
If more work is done on the system than heat added, the internal energy of the system will
actually decrease.
8. A great deal of effort, time, and money has been spent in the quest for a so-called perpetualmotion machine, which is defined as a hypothetical machine that operates or produces useful
work indefinitely and/or a hypothetical machine that produces more work or energy than it
consumes. Explain, in terms of the first law of thermodynamics, why or why not such a machine
is likely to be constructed.