Question 1

Rank from smallest to largest, the changes in entropy of a pan of water on a hot plate, as the temperature of the water

Accepted Answer

A) 1, 2, 3, 4 
B) 3, 4, 1, 2 
C) 1 and 2 tie, then 3 and 4 tie 
D) 3 and 4 tie, then 1 and 2 tie 
E) 4, 3, 2, 1 
A) 1, 2, 3, 4 
B) 3, 4, 1, 2 
C) 1 and 2 tie, then 3 and 4 tie 
D) 3 and 4 tie, then 1 and 2 tie 
E) 4, 3, 2, 1

Question 2

A Carnot heat engine operates between a hot reservoir at absolute temperature TH and a cold reservoir at absolute temperature TL.Its efficiency is:

Accepted Answer

A) TH/ TL 
B) TL /TH 
C) 1 - TH/ TL 
D) 1 - TL /TH 
E) 100% 
A) TH/ TL 
B) TL /TH 
C) 1 - TH/ TL 
D) 1 - TL /TH 
E) 100%

Question 3

Consider the following processes: The temperatures of two identical gases are increased from the same initial temperature to the same final temperature.Reversible processes are used.For gas A the process is carried out at constant volume while for gas B it is carried out at constant pressure.The change in entropy:

Accepted Answer

A) is the same for A and B 
B) is greater for A 
C) is greater for B 
D) is greater for A only if the initial temperature is low 
E) is greater for A only if the initial temperature is high 
A) is the same for A and B 
B) is greater for A 
C) is greater for B 
D) is greater for A only if the initial temperature is low 
E) is greater for A only if the initial temperature is high

Question 4

The temperature of n moles of a gas is increased from Ti to Tf at constant pressure.If the molar specific heat at constant pressure is Cp and is independent of temperature, then change in the entropy of the gas is:

Accepted Answer

A) nCp ln(Tf/Ti) 
B) nCp ln(Ti/Tf) 
C) nCp ln(Tf - Ti) 
D) nCp ln(1 - Ti/Tf) 
E) nCp (Tf - Ti) 
A) nCp ln(Tf/Ti) 
B) nCp ln(Ti/Tf) 
C) nCp ln(Tf - Ti) 
D) nCp ln(1 - Ti/Tf) 
E) nCp (Tf - Ti)

Question 5

According to the second law of thermodynamics:

Accepted Answer

A) heat energy cannot be completely converted to work 
B) work cannot be completely converted to heat energy 
C) for all cyclic processes we have dQ/T < 0 
D) the reason all heat engine efficiencies are less than 100% is friction, which is unavoidable 
E) all of the above are true 
A) heat energy cannot be completely converted to work 
B) work cannot be completely converted to heat energy 
C) for all cyclic processes we have dQ/T < 0 
D) the reason all heat engine efficiencies are less than 100% is friction, which is unavoidable 
E) all of the above are true

Question 6

A heat engine operates between a high temperature reservoir at TH and a low temperature reservoir at TL.Its efficiency is given by 1 - TL/TH:

Accepted Answer

A) only if the working substance is an ideal gas 
B) only if the engine is reversible 
C) only if the engine is quasi-static 
D) only if the engine operates on a Stirling cycle 
E) no matter what characteristics the engine has 
A) only if the working substance is an ideal gas 
B) only if the engine is reversible 
C) only if the engine is quasi-static 
D) only if the engine operates on a Stirling cycle 
E) no matter what characteristics the engine has

Question 7

A heat engine operates between 200 K and 100 K.In each cycle it takes 100 J from the hot reservoir, loses 25 J to the cold reservoir, and does 75 J of work.This heat engine violates:

Accepted Answer

A) both the first and second laws of thermodynamics 
B) the first law but not the second law of thermodynamics 
C) the second law but not the first law of thermodynamics 
D) neither the first law nor the second law of thermodynamics 
E) cannot answer without knowing the mechanical equivalent of heat 
A) both the first and second laws of thermodynamics 
B) the first law but not the second law of thermodynamics 
C) the second law but not the first law of thermodynamics 
D) neither the first law nor the second law of thermodynamics 
E) cannot answer without knowing the mechanical equivalent of heat

Question 8

Let SI  denote the change in entropy of a sample for an irreversible process from state A to state B.Let SR denote the change in entropy of the same sample for a reversible process from state A to state B.Then:

Accepted Answer

A) SI  > SR 
B) SI  = SR 
C) SI  R 
D) SI  = 0 
E) SR = 0 
A) SI  > SR 
B) SI  = SR 
C) SI  R 
D) SI  = 0 
E) SR = 0

Question 9

A refrigerator absorbs energy of magnitude $\vert$QL $\vert$as heat from a low temperature reservoir and rejects energy of magnitude $\vert$QH $\vert$ as heat to a high temperature reservoir.Work W is done on the working substance.The coefficient of performance is given by:

Accepted Answer

A) "$\vert$QL $\vert$/W" 
B) "$\vert$QH $\vert$/W" 
C) "($\vert$QL $\vert$ + $\vert$QH $\vert$)/W" 
D) "W/$\vert$QL $\vert$" 
E) "W/$\vert$QH $\vert$" 
A) "$\vert$QL $\vert$/W" 
B) "$\vert$QH $\vert$/W" 
C) "($\vert$QL $\vert$ + $\vert$QH $\vert$)/W" 
D) "W/$\vert$QL $\vert$" 
E) "W/$\vert$QH $\vert$"

Question 10

In a thermally insulated kitchen, an ordinary refrigerator is turned on and its door is left open.The temperature of the room:

Accepted Answer

A) remains constant according to the first law of thermodynamics 
B) increases according to the first law of thermodynamics 
C) decreases according to the first law of thermodynamics 
D) remains constant according to the second law of thermodynamics 
E) increases according to the second law of thermodynamics 
A) remains constant according to the first law of thermodynamics 
B) increases according to the first law of thermodynamics 
C) decreases according to the first law of thermodynamics 
D) remains constant according to the second law of thermodynamics 
E) increases according to the second law of thermodynamics

Question 11

A reversible refrigerator operates between a low temperature reservoir at TL and a high temperature reservoir at TH.Its coefficient of performance is given by:

Accepted Answer

A) (TH - TL)/ TL 
B) TL /(TH - TL) 
C) (TH - TL)/TH 
D) TH/(TH - TL) 
E) TH(TH + TL) 
A) (TH - TL)/ TL 
B) TL /(TH - TL) 
C) (TH - TL)/TH 
D) TH/(TH - TL) 
E) TH(TH + TL)

Question 12

An ideal gas, consisting of n moles, undergoes an irreversible process in which the temperature has the same value at the beginning and end.If the volume changes from Vi to Vf, the change in entropy is given by:

Accepted Answer

A) n R(Vf - Vi) 
B) n R ln(Vf - Vi) 
C) n R ln(Vi/Vf) 
D) n R ln(Vf/Vi) 
E) none of the above (entropy can't be calculated for an irreversible process) 
A) n R(Vf - Vi) 
B) n R ln(Vf - Vi) 
C) n R ln(Vi/Vf) 
D) n R ln(Vf/Vi) 
E) none of the above (entropy can't be calculated for an irreversible process)

Question 13

One mole of an ideal gas expands reversibly and isothermally at temperature T until its volume is doubled.The change of entropy of this gas for this process is:

Accepted Answer

A) R ln 2 
B) (ln 2)/T 
C) 0 
D) RT ln 2 
E) 2R 
A) R ln 2 
B) (ln 2)/T 
C) 0 
D) RT ln 2 
E) 2R

Question 14

A Carnot cycle:

Accepted Answer

A) is bounded by two isotherms and two adiabats on a p-V graph 
B) consists of two isothermal and two constant volume processes 
C) is any four sided process on a p-V graph 
D) only exists for an ideal gas 
E) has an efficiency equal to the enclosed area on a p-V diagram 
A) is bounded by two isotherms and two adiabats on a p-V graph 
B) consists of two isothermal and two constant volume processes 
C) is any four sided process on a p-V graph 
D) only exists for an ideal gas 
E) has an efficiency equal to the enclosed area on a p-V diagram

Question 15

A Carnot engine operates between 200 $\degree$C and 20 $\degree$C.Its maximum possible efficiency is:

Accepted Answer

A) 90% 
B) 100% 
C) 38% 
D) 72% 
E) 24% 
A) 90% 
B) 100% 
C) 38% 
D) 72% 
E) 24%

Question 16

An inventor suggests that a house might be heated by using a refrigerator to draw energy as heat from the ground and reject energy as heat into the house.He claims that the energy supplied to the house can exceed the work required to run the refrigerator.This:

Accepted Answer

A) is impossible by first law 
B) is impossible by second law 
C) would only work if the ground and the house were at the same temperature 
D) is impossible since heat flows from the (hot)house to the (cold)ground 
E) is possible 
A) is impossible by first law 
B) is impossible by second law 
C) would only work if the ground and the house were at the same temperature 
D) is impossible since heat flows from the (hot)house to the (cold)ground 
E) is possible

Question 17

Consider the following processes:   Which are never found to occur?

Accepted Answer

A) Only I 
B) Only II 
C) Only III 
D) Only II and III 
E) I, II and III 
A) Only I 
B) Only II 
C) Only III 
D) Only II and III 
E) I, II and III

Question 18

A heat engine that in each cycle does positive work and loses energy as heat, with no heat energy input, would violate:

Accepted Answer

A) the zeroth law of thermodynamics 
B) the first law of thermodynamics 
C) the second law of thermodynamics 
D) the third law of thermodynamics 
E) Newton's second law 
A) the zeroth law of thermodynamics 
B) the first law of thermodynamics 
C) the second law of thermodynamics 
D) the third law of thermodynamics 
E) Newton's second law

Question 19

A Carnot engine operates with a cold reservoir at a temperature of TL = 400 K and a hot reservoir at a temperature of TH = 500 K.What is the net entropy change as it goes through a complete cycle?

Accepted Answer

A) 0 J/K 
B) 20 J/K 
C) 80 J/K 
D) 400 J/K 
E) 500 J/K 
A) 0 J/K 
B) 20 J/K 
C) 80 J/K 
D) 400 J/K 
E) 500 J/K

Question 20

A cyclical process that transfers energy as heat from a high temperature reservoir to a low temperature reservoir with no other change would violate:

Accepted Answer

A) the zeroth law of thermodynamics 
B) the first law of thermodynamics 
C) the second law of thermodynamics 
D) the third law of thermodynamics 
E) none of the above 
A) the zeroth law of thermodynamics 
B) the first law of thermodynamics 
C) the second law of thermodynamics 
D) the third law of thermodynamics 
E) none of the above

Exam 20: Entropy and the Second Law of Thermodynamics

Rank from smallest to largest, the changes in entropy of a pan of water on a hot plate, as the temperature of the water

A Carnot heat engine operates between a hot reservoir at absolute temperature TH and a cold reservoir at absolute temperature TL.Its efficiency is:

The temperature of n moles of a gas is increased from Ti to Tf at constant pressure.If the molar specific heat at constant pressure is Cp and is independent of temperature, then change in the entropy of the gas is:

According to the second law of thermodynamics:

A heat engine operates between a high temperature reservoir at TH and a low temperature reservoir at TL.Its efficiency is given by 1 - TL/TH:

A heat engine operates between 200 K and 100 K.In each cycle it takes 100 J from the hot reservoir, loses 25 J to the cold reservoir, and does 75 J of work.This heat engine violates:

Let SI denote the change in entropy of a sample for an irreversible process from state A to state B.Let SR denote the change in entropy of the same sample for a reversible process from state A to state B.Then:

A refrigerator absorbs energy of magnitude ∣\vert∣ QL ∣\vert∣ as heat from a low temperature reservoir and rejects energy of magnitude ∣\vert∣ QH ∣\vert∣ as heat to a high temperature reservoir.Work W is done on the working substance.The coefficient of performance is given by:

In a thermally insulated kitchen, an ordinary refrigerator is turned on and its door is left open.The temperature of the room:

A reversible refrigerator operates between a low temperature reservoir at TL and a high temperature reservoir at TH.Its coefficient of performance is given by:

An ideal gas, consisting of n moles, undergoes an irreversible process in which the temperature has the same value at the beginning and end.If the volume changes from Vi to Vf, the change in entropy is given by:

One mole of an ideal gas expands reversibly and isothermally at temperature T until its volume is doubled.The change of entropy of this gas for this process is:

A Carnot cycle:

A Carnot engine operates between 200 °\degree° C and 20 °\degree° C.Its maximum possible efficiency is:

An inventor suggests that a house might be heated by using a refrigerator to draw energy as heat from the ground and reject energy as heat into the house.He claims that the energy supplied to the house can exceed the work required to run the refrigerator.This:

Consider the following processes: Which are never found to occur?

A heat engine that in each cycle does positive work and loses energy as heat, with no heat energy input, would violate:

A Carnot engine operates with a cold reservoir at a temperature of TL = 400 K and a hot reservoir at a temperature of TH = 500 K.What is the net entropy change as it goes through a complete cycle?

A cyclical process that transfers energy as heat from a high temperature reservoir to a low temperature reservoir with no other change would violate:

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A Carnot heat engine operates between a hot reservoir at absolute temperature T_H and a cold reservoir at absolute temperature T_L.Its efficiency is:

The temperature of n moles of a gas is increased from T_i to T_f at constant pressure.If the molar specific heat at constant pressure is C_p and is independent of temperature, then change in the entropy of the gas is:

A heat engine operates between a high temperature reservoir at T_H and a low temperature reservoir at T_L.Its efficiency is given by 1 - T_L/T_H:

Let S_I denote the change in entropy of a sample for an irreversible process from state A to state B.Let S_R denote the change in entropy of the same sample for a reversible process from state A to state B.Then:

A refrigerator absorbs energy of magnitude $\vert$ Q_L $\vert$ as heat from a low temperature reservoir and rejects energy of magnitude $\vert$ Q_H $\vert$ as heat to a high temperature reservoir.Work W is done on the working substance.The coefficient of performance is given by:

A reversible refrigerator operates between a low temperature reservoir at T_L and a high temperature reservoir at T_H.Its coefficient of performance is given by:

An ideal gas, consisting of n moles, undergoes an irreversible process in which the temperature has the same value at the beginning and end.If the volume changes from V_i to V_f, the change in entropy is given by:

A Carnot engine operates between 200 $\degree$ C and 20 $\degree$ C.Its maximum possible efficiency is:

A Carnot engine operates with a cold reservoir at a temperature of T_L = 400 K and a hot reservoir at a temperature of T_H = 500 K.What is the net entropy change as it goes through a complete cycle?