Question 1

Is it possible to transfer heat from a cold reservoir to a hot reservoir?

Accepted Answer

A)  No; this is forbidden by the second law of thermodynamics. 
B)  Yes; this will happen naturally. 
C)  Yes, but work will have to be done. 
D)  Theoretically yes, but it hasn't been accomplished yet. 
A)  No; this is forbidden by the second law of thermodynamics. 
B)  Yes; this will happen naturally. 
C)  Yes, but work will have to be done. 
D)  Theoretically yes, but it hasn't been accomplished yet.

Question 2

As a result of any natural process, the total entropy of any system plus that of its environment

Accepted Answer

A)  never decreases. 
B)  sometimes decreases. 
C)  never increases. 
D)  always stays the same. 
A)  never decreases. 
B)  sometimes decreases. 
C)  never increases. 
D)  always stays the same.

Question 3

A Carnot engine operates between a high temperature reservoir at 435 K and a river with water at 280 K. If it absorbs 3700 J of heat each cycle, how much work per cycle does it perform?

Accepted Answer

A)  1318 J 
B)  2382 J 
C)  1449 J 
D)  2251 J 
A)  1318 J 
B)  2382 J 
C)  1449 J 
D)  2251 J

Question 4

A 2.00 kg piece of lead at 40.0°C is placed in a very large quantity of water at 10.0°C, and thermal equilibrium is eventually reached. Calculate the entropy change of the lead that occurs during this process. The specific heat of lead is 130 J/(kg∙K).

Accepted Answer

A)  -12.5 J/K 
B)  86.0 J/K 
C)  -26.2 J/K 
D)  -86.0 J/K 
E)  -6.24 J/K 
A)  -12.5 J/K 
B)  86.0 J/K 
C)  -26.2 J/K 
D)  -86.0 J/K 
E)  -6.24 J/K

Question 5

During each cycle of operation, a refrigerator absorbs 230 J of heat from the freezer and expels 356 J of heat to the room. How much work input is required in each cycle?

Accepted Answer

A)  712 J 
B)  586 J 
C)  460 J 
D)  310 J 
E)  126 J 
A)  712 J 
B)  586 J 
C)  460 J 
D)  310 J 
E)  126 J

Question 6

The graph in the figure shows a cycle for a heat engine for which QH=35 J. What is the thermal efficiency of this engine?

Accepted Answer

A)  29 % 
B)  57 % 
C)  14 % 
D)  23 % 
A)  29 % 
B)  57 % 
C)  14 % 
D)  23 %

Question 7

A refrigerator has a coefficient of performance of 1.15, and it extracts 7.95 J of heat from the cold reservoir during each cycle.
(a) How much work is done on the gas in each cycle?
(b) How much heat is exhausted into the hot reservoir in each cycle?

Accepted Answer

(a) 6.91 J

Question 8

An ideal Carnot engine operates between reservoirs having temperatures of 125°C and -20°C. Each cycle the heat expelled by this engine is used to melt 30.0 g of ice at 0.00°C. The heat of fusion of water is 3.34 × 105 J/kg and the heat of vaporization of water is 2.25 × 106 J/kg.
(a) How much work does this engine do each cycle?
(b) How much heat per cycle does this engine absorb at the hot reservoir?

Accepted Answer

(a) 5740 J

Question 9

What is the change in entropy of 10.0 moles of ideal monatomic gas that reversibly undergoes the isothermal expansion shown in the figure? The ideal gas constant is R = 8.314 J/(mol∙K).

Accepted Answer

A)  221 J/K 
B)  104 J/K 
C)  63.1 J/K 
D)  45.2 J/K 
E)  90.8 J/K 
A)  221 J/K 
B)  104 J/K 
C)  63.1 J/K 
D)  45.2 J/K 
E)  90.8 J/K

Question 10

An engine manufacturer makes the claim that the engine they have developed will, on each cycle, take 100 J of heat out of boiling water at 100°C, do mechanical work of 80 J, and exhaust 20 J of heat at 10°C. What, if anything, is wrong with this claim?

Accepted Answer

A)  The heat exhausted must always be greater than the work done according to the second law of thermodynamics. 
B)  This engine violates the first law of thermodynamics because 100 J + 20 J ≠ 80 J. 
C)  An engine would operate by taking in heat at the lower temperature and exhausting heat at the higher temperature. 
D)  The efficiency of this engine is greater than the ideal Carnot cycle efficiency. 
E)  There is nothing wrong with this claim because 100 J = 20 J + 80 J. 
A)  The heat exhausted must always be greater than the work done according to the second law of thermodynamics. 
B)  This engine violates the first law of thermodynamics because 100 J + 20 J ≠ 80 J. 
C)  An engine would operate by taking in heat at the lower temperature and exhausting heat at the higher temperature. 
D)  The efficiency of this engine is greater than the ideal Carnot cycle efficiency. 
E)  There is nothing wrong with this claim because 100 J = 20 J + 80 J.

Question 11

A certain engine extracts 1300 J of heat from a hot temperature reservoir and discharges 700 J of heat to a cold temperature reservoir. What is the efficiency of this engine?

Accepted Answer

A)  46% 
B)  54% 
C)  86% 
D)  27% 
E)  13% 
A)  46% 
B)  54% 
C)  86% 
D)  27% 
E)  13%

Question 12

A Carnot refrigerator has a coefficient of performance of 2.5. The refrigerator consumes 50 W of power. How much heat is removed from the interior of the refrigerator in 1 hour?

Accepted Answer

A)  7.5 kJ 
B)  450 kJ 
C)  180 kJ 
D)  720 kJ 
E)  72 kJ 
A)  7.5 kJ 
B)  450 kJ 
C)  180 kJ 
D)  720 kJ 
E)  72 kJ

Question 13

A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the refrigerator in order to remove 250 J of heat from the interior?

Accepted Answer

A)  60 J 
B)  120 J 
C)  250 J 
D)  480 J 
E)  1050 J 
A)  60 J 
B)  120 J 
C)  250 J 
D)  480 J 
E)  1050 J

Question 14

You want to design an ideal Carnot heat engine that wastes only 35.0% of the heat that goes into it. The lowest cold-reservoir temperature available to you is +15.0°C. If 150.0 J of work is done per cycle, the heat input per cycle is closest to

Accepted Answer

A)  203 J 
B)  231 J 
C)  248 J 
D)  429 J 
E)  760 J 
A)  203 J 
B)  231 J 
C)  248 J 
D)  429 J 
E)  760 J

Question 15

One of the most efficient engines built so far has the following characteristics:
combustion chamber temperature = 1900°C
exhaust temperature = 430°C
7.0 × 109 cal of fuel produces 1.4 × 1010 J of work in one hour, where 1 cal = 4.19 J
(a) What is the actual efficiency of this engine?
(b) What is the Carnot efficiency of the engine?
(c) What is the power output of this engine?

Accepted Answer

(a) 48% 
(

Question 16

A nuclear fission power plant has an actual efficiency of 39%. If 0.25 MW of power are produced by the nuclear fission, how much electric power does the power plant output?

Accepted Answer

A)  0.098 MW 
B)  9.8 MW 
C)  35 MW 
D)  0.35 MW 
A)  0.098 MW 
B)  9.8 MW 
C)  35 MW 
D)  0.35 MW

Question 17

An air conditioner with a coefficient of performance of 3.5 uses 30 kW of power. How much power is it discharging to the outdoors?

Accepted Answer

A)  30 kW 
B)  75 kW 
C)  105 kW 
D)  135 kW 
E)  210 kW 
A)  30 kW 
B)  75 kW 
C)  105 kW 
D)  135 kW 
E)  210 kW

Question 18

A certain Carnot heat pump transfers energy from the outside of a house, where the temperature is -15°C, to the inside of a room where the temperature is 21°C. If this heat pump runs off of electricity, what is the minimum rate at which it uses electrical energy to deliver 150 W to the inside room?

Accepted Answer

The answer of A certain Carnot heat pump transfers energy...

Question 19

A Carnot engine is operated as a heat pump to heat a room in the winter. The heat pump delivers heat to the room at the rate of 34 kJ per second and maintains the room at a temperature of 293 K when the outside temperature is 229 K. The power requirement for the heat pump under these operating conditions is closest to

Accepted Answer

A)  7500 W. 
B)  6000 W. 
C)  17,000 W. 
D)  13,000 W. 
E)  9600 W. 
A)  7500 W. 
B)  6000 W. 
C)  17,000 W. 
D)  13,000 W. 
E)  9600 W.

Question 20

A 610-g quantity of an ideal gas undergoes a reversible isothermal compression at a temperature of 330 K. The compression reduces the volume of the gas from 0.40 m3 initially, to 0.21 m3 finally. The molecular mass of the gas is 33.0 g/mol and the ideal gas constant is R = 8.314 J/(mol∙K). The entropy change for the gas is closest to

Accepted Answer

A)  -99 J/K. 
B)  -81 J/K. 
C)  99 J/K. 
D)  81 J/K. 
E)  0.00 J/K. 
A)  -99 J/K. 
B)  -81 J/K. 
C)  99 J/K. 
D)  81 J/K. 
E)  0.00 J/K.

Exam 19: Heat Engines and Refrigerators

Is it possible to transfer heat from a cold reservoir to a hot reservoir?

As a result of any natural process, the total entropy of any system plus that of its environment

A Carnot engine operates between a high temperature reservoir at 435 K and a river with water at 280 K. If it absorbs 3700 J of heat each cycle, how much work per cycle does it perform?

A 2.00 kg piece of lead at 40.0°C is placed in a very large quantity of water at 10.0°C, and thermal equilibrium is eventually reached. Calculate the entropy change of the lead that occurs during this process. The specific heat of lead is 130 J/(kg∙K).

During each cycle of operation, a refrigerator absorbs 230 J of heat from the freezer and expels 356 J of heat to the room. How much work input is required in each cycle?

The graph in the figure shows a cycle for a heat engine for which QH=35 J. What is the thermal efficiency of this engine?

A refrigerator has a coefficient of performance of 1.15, and it extracts 7.95 J of heat from the cold reservoir during each cycle. (a) How much work is done on the gas in each cycle? (b) How much heat is exhausted into the hot reservoir in each cycle?

What is the change in entropy of 10.0 moles of ideal monatomic gas that reversibly undergoes the isothermal expansion shown in the figure? The ideal gas constant is R = 8.314 J/(mol∙K).

An engine manufacturer makes the claim that the engine they have developed will, on each cycle, take 100 J of heat out of boiling water at 100°C, do mechanical work of 80 J, and exhaust 20 J of heat at 10°C. What, if anything, is wrong with this claim?

A certain engine extracts 1300 J of heat from a hot temperature reservoir and discharges 700 J of heat to a cold temperature reservoir. What is the efficiency of this engine?

A Carnot refrigerator has a coefficient of performance of 2.5. The refrigerator consumes 50 W of power. How much heat is removed from the interior of the refrigerator in 1 hour?

A refrigerator has a coefficient of performance equal to 4.2. How much work must be done on the refrigerator in order to remove 250 J of heat from the interior?

You want to design an ideal Carnot heat engine that wastes only 35.0% of the heat that goes into it. The lowest cold-reservoir temperature available to you is +15.0°C. If 150.0 J of work is done per cycle, the heat input per cycle is closest to

A nuclear fission power plant has an actual efficiency of 39%. If 0.25 MW of power are produced by the nuclear fission, how much electric power does the power plant output?

An air conditioner with a coefficient of performance of 3.5 uses 30 kW of power. How much power is it discharging to the outdoors?

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The graph in the figure shows a cycle for a heat engine for which Q_H=35 J. What is the thermal efficiency of this engine?