1. Entropy
1 m3 of N2 gas is in a sealed container at room temperature. The gas increases its volume by two processes 1) isothermal expansion and 2) adiabatic expansion.
During 1) isothermal expansion the work done is W = -70,000 J.
During 2) adiabatic expansion the work done is W = -60,000 J.
What is the change in entropy for the two processes?
If the gas is now compressed back to its original volume using the same respective processes, what is the change in entropy?
What is the total change in entropy for expanding, then compressing back to the original volume?

2. Q20.2
An ideal gas is taken around the cycle shown in this pV–diagram, from a to b to c and back to a. Process b  c is isothermal. Which of the processes in this cycle could be reversible?
A. a  b
B. b  c
C. c  a
D. two or more of A., B., and C.
E. none of A., B., or C.

3. A20.2
An ideal gas is taken around the cycle shown in this pV–diagram, from a to b to c and back to a. Process b  c is isothermal. Which of the processes in this cycle could be reversible?
A. a  b
B. b  c
C. c  a
D. two or more of A., B., and C.
E. none of A., B., or C.

4. Q20.3
An ideal gas is taken around the cycle shown in this pV–diagram, from a to c to b and back to a. Process c  b is adiabatic. Which of the processes in this cycle could be reversible?
A. a  c
B. c  b
C. b  a
D. two or more of A., B., and C.
E. none of A., B., or C.

5. A20.3
An ideal gas is taken around the cycle shown in this pV–diagram, from a to c to b and back to a. Process c  b is adiabatic. Which of the processes in this cycle could be reversible?
A. a  c
B. c  b
C. b  a
D. two or more of A., B., and C.
E. none of A., B., or C.

6. Heat engines
As heat flows from a reservoir at higher temperature to a sink at lower temperature, work may be removed.
Even if no work is removed, maximum engine efficiencies never reach 100% and depend on Th and Tc .

7. Q20.4
During one cycle, an automobile engine takes in 12,000 J of heat and discards 9000 J of heat. What is the efficiency of this engine?
A. 400%
B. 133%
C. 75%
D. 33%
E. 25%

8. A20.4
During one cycle, an automobile engine takes in 12,000 J of heat and discards 9000 J of heat. What is the efficiency of this engine?
A. 400%
B. 133%
C. 75%
D. 33%
E. 25%

9. Q20.5
During one cycle, an automobile engine with an efficiency of 20% takes in 10,000 J of heat. How much work does the engine do per cycle?
A J
B J
C J
D J
E. 400 J

10. A20.5
During one cycle, an automobile engine with an efficiency of 20% takes in 10,000 J of heat. How much work does the engine do per cycle?
A J
B J
C J
D J
E. 400 J

11. Analyze heat engine
A gasoline engine in a truck takes in 10,000 J of heat and delivers 2000 J of mechanical work per cycle. The heat is obtained by burning gasoline with heat of combustion Lc = 5.0 x 104 J/g.
Draw heat engine diagram
What is the thermal efficiency of this engine?
How much heat is discarded in each cycle?
How much gasoline is burned in each cycle?
If the engine goes through 25 cycles per second, what is its power output in watts?

12. The internal-combustion engine
A fuel vapor can be compressed, then detonated to rebound the cylinder, doing useful work.

13. The Otto cycle and the Diesel cycle
A fuel vapor can be compressed, then detonated to rebound the cylinder, doing useful work.

14. Refrigerators
A refrigerator is essentially a heat engine running backwards.

15. Air conditioning, the clever placement of an air conditioner

16. The Second Law stated in practical terms
You can’t make a machine that does nothing but move heat from a cold item to a hot sink.

17. Q20.6
A copper pot at room temperature is filled with room-temperature water. Imagine a process whereby the water spontaneously freezes and the pot becomes hot. Why is such a process impossible?
A. It violates the first law of thermodynamics.
B. It violates the second law of thermodynamics.
C. It violates both the first and second laws of thermodynamics.
D. none of the above

18. A20.6
A copper pot at room temperature is filled with room-temperature water. Imagine a process whereby the water spontaneously freezes and the pot becomes hot. Why is such a process impossible?
A. It violates the first law of thermodynamics.
B. It violates the second law of thermodynamics.
C. It violates both the first and second laws of thermodynamics.
D. none of the above

19. The Carnot Cycle
A thought experiment envisioning the most efficient heat engine that might be created.
Reversible processes of isothermal expansion, adiabatic expansion, isothermal compression, then finally adiabatic compression.

20. Q20.7
A Carnot engine takes heat in from a reservoir at 400 K and discards heat to a reservoir at 300 K.
If the engine does 12,000 J of work per cycle, how much heat does it take in per cycle?
A. 48,000 J
B. 24,000 J
C. 16,000 J
D J
E. none of the above

21. A20.7
A Carnot engine takes heat in from a reservoir at 400 K and discards heat to a reservoir at 300 K.
If the engine does 12,000 J of work per cycle, how much heat does it take in per cycle?
A. 48,000 J
B. 24,000 J
C. 16,000 J
D J
E. none of the above

22. Analysis of Carnot Cycles
Follow Example 20.2 and Figure
Follow Example 20.3.