Question 1

A refrigerator has a coefficient of performance of 4. If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle, the heat expelled (in cal) into the heat reservoir is

Accepted Answer

A)  40.5 
B)  37.5 
C)  36.5 
D)  34.5 
E)  22.5

Question 2

Which answer below is not a statement of the second law of thermodynamics?

Accepted Answer

A)  Real processes proceed in a preferred direction. 
B)  Energy does not flow spontaneously by heat from a cold to a hot reservoir. 
C)  The entropy of the universe increases in all natural processes. 
D)  In theory, heat engines working in a cycle employ reversible processes. 
E)  You cannot construct a heat engine, operating in a cycle that does nothing but take heat from a reservoir and perform an equal amount of work.

Question 3

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle. The amount of heat expelled in each cycle is

Accepted Answer

A)  1 000 J 
B)  1 500 J 
C)  2 000 J 
D)  500 J 
E)  3 000 J

Question 4

Find the change in entropy (in J/K) when 5.00 moles of an ideal monatomic gas are allowed to expand isobarically from an initial volume of 20 cm3 to a final volume of 100 cm3.

Accepted Answer

A)  167 
B)  100 
C)  67 
D)  52 
E)  152

Question 5

A lawn mower has a 6-horsepower engine (1 HP = 750 W). If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is

Accepted Answer

A)  1 800 J 
B)  2 000 J 
C)  2 200 J 
D)  2 400 J 
E)  2 250 J

Question 6

For the same temperature increase in a system, the change in entropy, ΔS, is largest in a reversible

Accepted Answer

A)  constant volume process. 
B)  constant pressure process. 
C)  adiabatic process. 
D)  process in which no heat is transferred. 
E)  process in which no work is performed.

Question 7

When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is

Accepted Answer

A)  cm ln(T2/T1) 
B)  cm (T2/T1) 
C)  cm (T2 − T1)/T1 
D)  cm (T2 − T1)/T2 
E)  cm (T2 − T1)/(T2 + T1)

Question 8

Ten kilograms of water at 0°C is mixed with 10 kg of water at 100°C. The change in entropy (in cal/K) of the system is

Accepted Answer

A)  1 000 
B)  480 
C)  −720 
D)  240 
E)  −168

Question 9

Exactly 500 grams of ice are melted at a temperature of 32°F. (Lice = 333 J/g.) The change in entropy (in J/K) is

Accepted Answer

A)  321 
B)  146 
C)  512 
D)  610 
E)  5 230

Question 10

Suppose there are 3 molecules in a container. If each molecule has a 1-in-2 chance of being in the left half of the container, what is the probability that there are exactly 2 molecules in the left half of the container?

Accepted Answer

A)  1/2 
B)  1/3 
C)  1/8 
D)  3/8 
E)  3/5

Question 11

Selena states that  proves that entropy has a definite value at the beginning and end of an adiabatic free expansion. Ron says  , where W is the number of microstates of a given macrostate. Which one, if either, is correct?

Accepted Answer

A)  Only Selena, because entropy can depend only on macroscopic variables. 
B)  Only Ron, because entropy can depend only on microscopic variables. 
C)  Only Selena, because
 in an adiabatic free expansion. 
D)  Neither, because we cannot calculate changes in entropy in an adiabatic free expansion. 
E)  Both, because entropy, which is macroscopic is a function of microscopic disorder.

Question 12

An ideal gas is allowed to expand adiabatically. Assume the process is reversible. The change in entropy is

Accepted Answer

A)  0 
B)  nR ln (V2/V1) 
C)  nR ln (T2/T1) 
D)  kn ln (V2/V1) 
E)  kn ln (T2/T1)

Question 13

The change in entropy when 1 kg of ice melts at 0°C is (in J/K). (Lice = 333 J/g.)

Accepted Answer

A)  335. 
B)  603. 
C)  1 220. 
D)  1 310. 
E)  2 160.

Question 14

In an engine operating in the Otto cycle, the final volume of the fuel-air mixture is one sixth the initial volume. Assume γ = 1.4. The maximum theoretical efficiency of this cycle, in per cent, is

Accepted Answer

A)  17. 
B)  49. 
C)  51. 
D)  56. 
E)  83.

Question 15

Which of the following is an almost reversible process?

Accepted Answer

A)  The explosion of hydrogen and oxygen to form water. 
B)  Heat transfer through thick insulation. 
C)  The adiabatic free expansion of a gas. 
D)  A slow isothermal compression of a gas. 
E)  A slow leakage of gas into an empty chamber through a small hole in a membrane.

Question 16

Since Lice = 333 J/g, the change in entropy (in cal/K) when 1.00 kg of ice melts is

Accepted Answer

A)  144 
B)  291 
C)  312 
D)  516 
E)  80

Question 17

A vessel containing 5.0 kg of water at 10°C is put into a refrigerator. The 1/7 HP motor (1 HP = 746 W) runs for 5.0 minutes to cool the liquid to the refrigerator's low temperature, 0°C. What is the κ of the refrigerator?

Accepted Answer

A)  5.7 
B)  4.6 
C)  6.5 
D)  7.2 
E)  3.6

Question 18

If n moles of an ideal gas are compressed isothermally from an initial volume V1 to a final volume V2, the change in entropy is

Accepted Answer

A)  nR ln (V2/V1) 
B)  nRT ln (V2/V1) 
C)  nkB ln (V2/V1) 
D) 
 
E)  n Cv/T

Question 19

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle, the heat expelled (in cal) to the warm indoors is

Accepted Answer

A)  34 
B)  27 
C)  36 
D)  40 
E)  80

Question 20

A violation of the second law of thermodynamics would occur if

Accepted Answer

A)  a ball lying on the ground started to bounce. 
B)  transfer of energy by heat moved energy from an object at low temperature to an object at a higher temperature. 
C)  a motion picture was run backwards through the projector. 
D)  any of the above occurred. 
E)  (a) or (b) occurred, but not (c).

Exam 22: Heat Engines, Entropy, and the Second Law of Thermodynamics

A refrigerator has a coefficient of performance of 4. If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle, the heat expelled (in cal) into the heat reservoir is

Which answer below is not a statement of the second law of thermodynamics?

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle. The amount of heat expelled in each cycle is

Find the change in entropy (in J/K) when 5.00 moles of an ideal monatomic gas are allowed to expand isobarically from an initial volume of 20 cm³ to a final volume of 100 cm³.

A lawn mower has a 6-horsepower engine (1 HP = 750 W) . If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is

For the same temperature increase in a system, the change in entropy, ΔS, is largest in a reversible

When water of mass m and specific heat c is heated from absolute temperature T₁ to absolute temperature T₂, its change in entropy is

Ten kilograms of water at 0°C is mixed with 10 kg of water at 100°C. The change in entropy (in cal/K) of the system is

Exactly 500 grams of ice are melted at a temperature of 32°F. (L_ice = 333 J/g.) The change in entropy (in J/K) is

Suppose there are 3 molecules in a container. If each molecule has a 1-in-2 chance of being in the left half of the container, what is the probability that there are exactly 2 molecules in the left half of the container?

Selena states that proves that entropy has a definite value at the beginning and end of an adiabatic free expansion. Ron says , where W is the number of microstates of a given macrostate. Which one, if either, is correct?

An ideal gas is allowed to expand adiabatically. Assume the process is reversible. The change in entropy is

The change in entropy when 1 kg of ice melts at 0°C is (in J/K) . (L_ice = 333 J/g.)

In an engine operating in the Otto cycle, the final volume of the fuel-air mixture is one sixth the initial volume. Assume γ = 1.4. The maximum theoretical efficiency of this cycle, in per cent, is

Which of the following is an almost reversible process?

Since L_ice = 333 J/g, the change in entropy (in cal/K) when 1.00 kg of ice melts is

A vessel containing 5.0 kg of water at 10°C is put into a refrigerator. The 1/7 HP motor (1 HP = 746 W) runs for 5.0 minutes to cool the liquid to the refrigerator's low temperature, 0°C. What is the κ of the refrigerator?

If n moles of an ideal gas are compressed isothermally from an initial volume V₁ to a final volume V₂, the change in entropy is

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle, the heat expelled (in cal) to the warm indoors is

A violation of the second law of thermodynamics would occur if

Exam 22: Heat Engines, Entropy, and the Second Law of Thermodynamics

A refrigerator has a coefficient of performance of 4. If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle, the heat expelled (in cal) into the heat reservoir is

Which answer below is not a statement of the second law of thermodynamics?

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle. The amount of heat expelled in each cycle is

Find the change in entropy (in J/K) when 5.00 moles of an ideal monatomic gas are allowed to expand isobarically from an initial volume of 20 cm3 to a final volume of 100 cm3.

A lawn mower has a 6-horsepower engine (1 HP = 750 W) . If the engine has an efficiency of 20%, and the throttle is such that the engine cycles 10 times a second, the heat that is expelled in one cycle is

For the same temperature increase in a system, the change in entropy, ΔS, is largest in a reversible

When water of mass m and specific heat c is heated from absolute temperature T1 to absolute temperature T2, its change in entropy is

Ten kilograms of water at 0°C is mixed with 10 kg of water at 100°C. The change in entropy (in cal/K) of the system is

Exactly 500 grams of ice are melted at a temperature of 32°F. (Lice = 333 J/g.) The change in entropy (in J/K) is

Suppose there are 3 molecules in a container. If each molecule has a 1-in-2 chance of being in the left half of the container, what is the probability that there are exactly 2 molecules in the left half of the container?

Selena states that proves that entropy has a definite value at the beginning and end of an adiabatic free expansion. Ron says , where W is the number of microstates of a given macrostate. Which one, if either, is correct?

An ideal gas is allowed to expand adiabatically. Assume the process is reversible. The change in entropy is

The change in entropy when 1 kg of ice melts at 0°C is (in J/K) . (Lice = 333 J/g.)

In an engine operating in the Otto cycle, the final volume of the fuel-air mixture is one sixth the initial volume. Assume γ = 1.4. The maximum theoretical efficiency of this cycle, in per cent, is

Which of the following is an almost reversible process?

Since Lice = 333 J/g, the change in entropy (in cal/K) when 1.00 kg of ice melts is

A vessel containing 5.0 kg of water at 10°C is put into a refrigerator. The 1/7 HP motor (1 HP = 746 W) runs for 5.0 minutes to cool the liquid to the refrigerator's low temperature, 0°C. What is the κ of the refrigerator?

If n moles of an ideal gas are compressed isothermally from an initial volume V1 to a final volume V2, the change in entropy is

A heat pump has a coefficient of performance of 4. If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle, the heat expelled (in cal) to the warm indoors is

A violation of the second law of thermodynamics would occur if

Find the change in entropy (in J/K) when 5.00 moles of an ideal monatomic gas are allowed to expand isobarically from an initial volume of 20 cm³ to a final volume of 100 cm³.

When water of mass m and specific heat c is heated from absolute temperature T₁ to absolute temperature T₂, its change in entropy is

Exactly 500 grams of ice are melted at a temperature of 32°F. (L_ice = 333 J/g.) The change in entropy (in J/K) is

The change in entropy when 1 kg of ice melts at 0°C is (in J/K) . (L_ice = 333 J/g.)

Since L_ice = 333 J/g, the change in entropy (in cal/K) when 1.00 kg of ice melts is

If n moles of an ideal gas are compressed isothermally from an initial volume V₁ to a final volume V₂, the change in entropy is