Q: A 1.00 kg block of ice at $$0^\circC $$melts to water at $$0^\circC. If $$the latent heat of fusion for ice is $$L_f = 3.34 \times 10^5$\ \mathrm{J/kg}$$, what is the change in entropy?

$$\Delta S = \frac{Q}{T} = \frac{3.34 \times 10^5$}{273} \approx 1220\ \mathrm{J/K}$$

Question 1

Which of the following best describes a reversible process in thermodynamics?

Accepted Answer

A process that can be completely undone, with the system remaining in thermal and mechanical equilibrium throughout.

Question 2

A heat engine absorbs $$Q_H = 2500\ \mathrm{J} of $$heat and does $$W = 500\ \mathrm{J} of $$work per cycle. What is the thermal efficiency $$e of $$this engine?

Accepted Answer

$$e = 0.2$$

Question 3

For a Carnot engine operating between a hot reservoir at $$T_H = 500\ \mathrm{K}$$ and a cold reservoir at $$T_C = 300\ \mathrm{K}$$, what is the maximum possible efficiency?

Accepted Answer

$$e_{Carnot} = 1 - \frac{T_C}{T_H} = 1 - \frac{300}{500} = 0.4$$

Question 4

Which statement is a direct consequence of the second law of thermodynamics?

Accepted Answer

The entropy of an isolated system can never decrease over time.

Question 5

A refrigerator removes $$Q_C = 100\ \mathrm{J} of $$heat from its interior and requires $$W = 25\ \mathrm{J} of $$work. What is its coefficient of performance $$K$$?

Accepted Answer

$$K = \frac{Q_C}{W} = \frac{100}{25} = 4$$

Question 6

For a reversible isothermal process, the change in entropy $$\Delta S is $$given by:

Accepted Answer

$$\Delta S = \frac{Q}{T}$$

Question 7

Which of the following is NOT a consequence of $$\Delta S_{net} \geq 0$$?

Accepted Answer

A house of cards will spontaneously assemble itself.

Question 8

A Carnot refrigerator operates between $$T_H = 350\ \mathrm{K}$$ and $$T_C = 300\ \mathrm{K}. $$What is its coefficient of performance $$K_{Carnot}$$?

Accepted Answer

$$K_{Carnot} = \frac{T_C}{T_H - T_C} = \frac{300}{350 - 300} = 6$$

Question 9

Which of the following best describes entropy?

Accepted Answer

A quantitative measure of how disordered a system is.

Question 10

For a cyclic process, which of the following is true?

Accepted Answer

$$\Delta U = Q - W = 0$$

Question 11

A heat engine absorbs $$Q_H$$ from a hot reservoir and expels $$Q_C to a $$cold reservoir. Which equation correctly relates these quantities to the work done $$W$$?

Accepted Answer

$$W = Q_H - |Q_C|$$

Question 12

Which of the following statements about the Carnot cycle is correct?

Accepted Answer

It is the most efficient heat engine possible, but not practical for real engines.

Question 13

If $$Q = 0$$ and $$\Delta S = 0$$ for a process, what type of process is this?

Accepted Answer

A reversible adiabatic process

Question 14

A 1.00 kg block of ice at $$0^\circC $$melts to water at $$0^\circC. If $$the latent heat of fusion for ice is $$L_f = 3.34 	imes 10^5$\ \mathrm{J/kg}$$, what is the change in entropy?

Accepted Answer

$$\Delta S = \frac{Q}{T} = \frac{3.34 	imes 10^5$}{273} \approx 1220\ \mathrm{J/K}$$

Question 15

Which of the following is a correct statement of the second law of thermodynamics for refrigerators?

Accepted Answer

It is impossible for any process to have as its sole result the transfer of heat from a cooler to a hotter object.

Question 16

The efficiency of an internal combustion engine is most closely related to which parameter?

Accepted Answer

The compression ratio $$R = \frac{V_2$}{V_1$}$$

Question 17

Which of the following is true for a Carnot engine operating between two reservoirs?

Accepted Answer

Its efficiency depends only on the temperatures of the hot and cold reservoirs.

Question 18

Which law of thermodynamics is summarized by the phrase, 'You can't break even'?

Accepted Answer

Second law of thermodynamics

Question 19

If a heat engine absorbs $$Q_H = 1000\ \mathrm{J}$$ and expels $$Q_C = 700\ \mathrm{J}$$, how much work does it do per cycle?

Accepted Answer

$$W = Q_H - Q_C = 300\ \mathrm{J}$$

Chapter 16: The Second Law of Thermodynamics – Heat Engines, Entropy, and the Carnot Cycle

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