Question 1

If you run a refrigerator in a closed room with the door to the refrigerator open,the temperature of the room

Accepted Answer

A) increases. 
B) remains the same. 
C) decreases. 
D) Any of these can happen depending on how efficient the refrigerator is. 
E) Any of these can happen depending on the relative sizes of the room and the refrigerator.

Question 2

What is the maximum possible coefficient of performance of a heat pump that is capable of maintaining the interior of a house at +20ºC when the temperature outside is -40ºC?

Accepted Answer

A) 2.0 
B) 5.2 
C) 12 
D) 4.9 
E) 3.9

Question 3

An electric power plant generates 100 MW of power at an efficiency of 35%.At what rate must water be circulated pass the condenser if the change in water temperature is not to exceed 10ºC?

Accepted Answer

A) 2400 kg/s 
B) 6800 kg/s 
C) 3400 kg/s 
D) 11300 kg/s 
E) 4400 kg/s

Question 4

The construction of a heat engine operating between temperatures T1 and T2,and having an efficiency greater than that of a Carnot engine operating between the same two temperatures,would constitute a violation of

Accepted Answer

A) the law of the conservation of energy. 
B) the first law of thermodynamics. 
C) the second law of thermodynamics. 
D) Boyle's law. 
E) None of these is correct.

Question 5

A heat engine with an output of 300 W has an efficiency of 25% and works at 10 cycles/s.How much heat is absorbed (Qh)and how much rejected (Qc)in each cycle?

Accepted Answer

A) Qh = 150 J,Qc = 120 J 
B) Qh = 1500 J,Qc = 1200 J 
C) Qh = 40 J,Qc = 10 J 
D) Qh = 120 J,Qc = 90 J 
E) Qh = 1200 J,Qc = 900 J

Question 6

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.What is the change in the entropy of the universe when this plant does 1.0 kJ of work?

Accepted Answer

A) 16 J/K 
B) 1.7 J/K 
C) 55 J/K 
D) 1.7 mJ/K 
E) 0.85 J/K

Question 7

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.How much heat is rejected to the cold reservoir in doing 1.0 kJ of work?

Accepted Answer

A) 3.8 kJ 
B) 0.83 kJ 
C) 2.8 kJ 
D) 1.8 kJ 
E) 0.67 kJ

Question 8

A refrigerator with a coefficient of performance 5.0 removes 25 kJ of heat from a cold reservoir.If this refrigerator is reversible and is run backward as a heat engine,what would be the efficiency of the heat engine?

Accepted Answer

A) 50% 
B) 80% 
C) 83% 
D) 17% 
E) 20%

Question 9

The efficiency of a Carnot engine operating between 300º C and 250ºC is about

Accepted Answer

A) 83% 
B) 17% 
C) 57% 
D) 43% 
E) 9%

Question 10

Use the following diagram to answer the next problem. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at 
TS1U1B1HS1U1B0 = 400 K and cold reservoir at TS1U1B1LS1U1B0 = 300 K, in a cycle from a→b→c→d→a. From a→b the gas undergoes an isothermal expansion, changing its volume from Va to 2.5Va. From b→c, the pressure is reduced at a constant volume. From c→d, the gas undergoes an isothermal compression, and from d→a, the pressure is increased at a constant volume until the gas is back at the original condition at a.

-How much work is obtained from the engine in each cycle?

Accepted Answer

A) 22.9 J 
B) 30.5 J 
C) 7.62 J 
D) 8.31 J 
E) 0.917 J

Question 11

Two refrigerators,one with a COP of 4.0 and another with a COP of 5.0,both extract 400 kJ of heat from the cold reservoir (food).Calculate the difference in energy they exhaust to the hot reservoir and hence the room.

Accepted Answer

A) 320 kJ 
B) 80 kJ 
C) 125 kJ 
D) 100 kJ 
E) 20 kJ

Question 12

Use the following diagram to answer the next problem. An ideal heat engine uses 0.01 mol of gas and operates between a hot reservoir at 
TS1U1B1HS1U1B0 = 400 K and cold reservoir at TS1U1B1LS1U1B0 = 300 K, in a cycle from a→b→c→d→a. From a→b the gas undergoes an isothermal expansion, changing its volume from Va to 2.5Va. From b→c, the pressure is reduced at a constant volume. From c→d, the gas undergoes an isothermal compression, and from d→a, the pressure is increased at a constant volume until the gas is back at the original condition at a.

-If the engine operates at 50 cycles per second,the power output is

Accepted Answer

A) 381 W 
B) 45.8 W 
C) 1145 W 
D) 415 W 
E) 1525 W

Question 13

A heat engine absorbs 64 kcal of heat from a hot reservoir and exhausts 42 kcal to a cold reservoir each cycle.Its efficiency is

Accepted Answer

A) 30% 
B) 34% 
C) 38% 
D) 40% 
E) 42%

Question 14

A refrigerator has a coefficient of performance 4.0.How much heat is exhausted to the hot reservoir when 400 kJ of heat are removed from the cold reservoir?

Accepted Answer

A) 500 kJ 
B) 400 kJ 
C) 100 kJ 
D) 80 kJ 
E) Not enough information is given to answer this question.

Question 15

A substance undergoes a series of reversible processes that bring it back to its initial state.In this cycle,heat Qx is absorbed by the substance and heat Qy is rejected.The net amount of work performed by the substance is

Accepted Answer

A) Qy - Qx  
B) Qx - Qy  
C) (Qy - Qx)/Qy  
D) (Qx - Qy)/Qx  
E) (Qx - Qy)/Qy

Question 16

A heat engine operating between the temperatures T1 and T2 takes in Q1 calories at temperature T1 and gives up Q2 calories at temperature T2.The efficiency of this heat engine is

Accepted Answer

A) (Q1 - Q2)/Q2  
B) (Q1 - Q2)/Q1  
C) (T2 - T1)/T2  
D) Q2/(Q1 - Q2) 
E) T1/(T1 - T2)

Question 17

A heat pump needs to supply 20 kW of power to maintain the inside temperature of a house at 25S1U1P1$\circ$S1S1P0C while the outside temperature is 0S1U1P1$\circ$S1S1P0C.What is the savings in the electric bill per month by using the heat pump instead of direct electrical heating? Assume that the heat pump/direct heating is on for 4 hours per day and 1 kW.hr costs $0.10.

Accepted Answer

A) $220 
B) $20.2 
C) $200 
D) $40.4 
E) $80.8

Question 18

For which of the following is COP the abbreviation?

Accepted Answer

A) Clausius or Planck 
B) cycle of pressure 
C) coefficients of pressure 
D) Carnot ordered performance 
E) coefficient of performance

Question 19

A container has 0.2 mole of O2 gas and the gas is heated from 0S1U1P1$\circ$S1S1P0C to 100S1U1P1$\circ$S1S1P0C.What is the change in entropy of the gas? (R = 8.314 J/mol·K)

Accepted Answer

A) 1.82 J/K 
B) 1.30 J/K 
C) 0.78 J/K 
D) 26.8 J/K 
E) zero

Exam 19: The Second Law of Thermodynamics

If you run a refrigerator in a closed room with the door to the refrigerator open,the temperature of the room

What is the maximum possible coefficient of performance of a heat pump that is capable of maintaining the interior of a house at +20ºC when the temperature outside is -40ºC?

An electric power plant generates 100 MW of power at an efficiency of 35%.At what rate must water be circulated pass the condenser if the change in water temperature is not to exceed 10ºC?

The construction of a heat engine operating between temperatures T₁ and T₂,and having an efficiency greater than that of a Carnot engine operating between the same two temperatures,would constitute a violation of

A heat engine with an output of 300 W has an efficiency of 25% and works at 10 cycles/s.How much heat is absorbed (Q_h) and how much rejected (Q_c) in each cycle?

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.What is the change in the entropy of the universe when this plant does 1.0 kJ of work?

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.How much heat is rejected to the cold reservoir in doing 1.0 kJ of work?

A refrigerator with a coefficient of performance 5.0 removes 25 kJ of heat from a cold reservoir.If this refrigerator is reversible and is run backward as a heat engine,what would be the efficiency of the heat engine?

The efficiency of a Carnot engine operating between 300º C and 250ºC is about

Two refrigerators,one with a COP of 4.0 and another with a COP of 5.0,both extract 400 kJ of heat from the cold reservoir (food) .Calculate the difference in energy they exhaust to the hot reservoir and hence the room.

A heat engine absorbs 64 kcal of heat from a hot reservoir and exhausts 42 kcal to a cold reservoir each cycle.Its efficiency is

A refrigerator has a coefficient of performance 4.0.How much heat is exhausted to the hot reservoir when 400 kJ of heat are removed from the cold reservoir?

A substance undergoes a series of reversible processes that bring it back to its initial state.In this cycle,heat Q_x is absorbed by the substance and heat Q_y is rejected.The net amount of work performed by the substance is

A heat engine operating between the temperatures T₁ and T₂ takes in Q₁ calories at temperature T₁ and gives up Q₂ calories at temperature T₂.The efficiency of this heat engine is

For which of the following is COP the abbreviation?

A container has 0.2 mole of O₂ gas and the gas is heated from 0^$\circ$C to 100^$\circ$C.What is the change in entropy of the gas? (R = 8.314 J/mol·K)

Exam 19: The Second Law of Thermodynamics

If you run a refrigerator in a closed room with the door to the refrigerator open,the temperature of the room

What is the maximum possible coefficient of performance of a heat pump that is capable of maintaining the interior of a house at +20ºC when the temperature outside is -40ºC?

An electric power plant generates 100 MW of power at an efficiency of 35%.At what rate must water be circulated pass the condenser if the change in water temperature is not to exceed 10ºC?

The construction of a heat engine operating between temperatures T1 and T2,and having an efficiency greater than that of a Carnot engine operating between the same two temperatures,would constitute a violation of

A heat engine with an output of 300 W has an efficiency of 25% and works at 10 cycles/s.How much heat is absorbed (Qh) and how much rejected (Qc) in each cycle?

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.What is the change in the entropy of the universe when this plant does 1.0 kJ of work?

A steam power plant with an efficiency of 65% of the maximum thermodynamic efficiency operates between 250º C and 40ºC.How much heat is rejected to the cold reservoir in doing 1.0 kJ of work?

A refrigerator with a coefficient of performance 5.0 removes 25 kJ of heat from a cold reservoir.If this refrigerator is reversible and is run backward as a heat engine,what would be the efficiency of the heat engine?

The efficiency of a Carnot engine operating between 300º C and 250ºC is about

Two refrigerators,one with a COP of 4.0 and another with a COP of 5.0,both extract 400 kJ of heat from the cold reservoir (food) .Calculate the difference in energy they exhaust to the hot reservoir and hence the room.

A heat engine absorbs 64 kcal of heat from a hot reservoir and exhausts 42 kcal to a cold reservoir each cycle.Its efficiency is

A refrigerator has a coefficient of performance 4.0.How much heat is exhausted to the hot reservoir when 400 kJ of heat are removed from the cold reservoir?

A substance undergoes a series of reversible processes that bring it back to its initial state.In this cycle,heat Qx is absorbed by the substance and heat Qy is rejected.The net amount of work performed by the substance is

A heat engine operating between the temperatures T1 and T2 takes in Q1 calories at temperature T1 and gives up Q2 calories at temperature T2.The efficiency of this heat engine is

For which of the following is COP the abbreviation?

A container has 0.2 mole of O2 gas and the gas is heated from 0 ∘\circ∘ C to 100 ∘\circ∘ C.What is the change in entropy of the gas? (R = 8.314 J/mol·K)

The construction of a heat engine operating between temperatures T₁ and T₂,and having an efficiency greater than that of a Carnot engine operating between the same two temperatures,would constitute a violation of

A heat engine with an output of 300 W has an efficiency of 25% and works at 10 cycles/s.How much heat is absorbed (Q_h) and how much rejected (Q_c) in each cycle?

A substance undergoes a series of reversible processes that bring it back to its initial state.In this cycle,heat Q_x is absorbed by the substance and heat Q_y is rejected.The net amount of work performed by the substance is

A heat engine operating between the temperatures T₁ and T₂ takes in Q₁ calories at temperature T₁ and gives up Q₂ calories at temperature T₂.The efficiency of this heat engine is

A container has 0.2 mole of O₂ gas and the gas is heated from 0^$\circ$C to 100^$\circ$C.What is the change in entropy of the gas? (R = 8.314 J/mol·K)