Question 1

A sample of ideal gas undergoes an isothermal expansion from volume $$V_1 to$$ $$V_2 at $$temperature $$T. $$Which of the following statements is correct regarding the change in internal energy ($$\Delta U$$), heat ($$Q$$), and work ($$W) $$for this process?

Accepted Answer

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

Question 2

A heat engine absorbs $$800\ \mathrm{J} of $$heat from a hot reservoir and exhausts $$500\ \mathrm{J} to a $$cold reservoir in each cycle. What is the efficiency $$e of $$this engine?

Accepted Answer

$$e = 0.625$$

Question 3

Which of the following best describes an adiabatic process for an ideal gas?

Accepted Answer

No heat is exchanged with the surroundings ($$Q = 0)$$

Question 4

A refrigerator removes $$200\ \mathrm{J} of $$heat from its cold compartment using $$50\ \mathrm{J} of $$work per cycle. What is its coefficient of performance (COP)?

Accepted Answer

$$\mathrm{COP} = 4$$

Question 5

Which of the following statements about entropy is TRUE?

Accepted Answer

For any real (irreversible) process, the total entropy of the universe increases ($$\Delta S_{tot} \u003e 0)$$

Question 6

A Carnot engine operates between a hot reservoir at $$T_H = 500\ \mathrm{K}$$ and a cold reservoir at $$T_L = 300\ \mathrm{K}. $$What is the maximum possible efficiency of this engine?

Accepted Answer

$$e_{max} = 0.4$$

Question 7

During a free expansion of an ideal gas into a vacuum (no external pressure), which of the following is true?

Accepted Answer

No work is done and no heat is exchanged; internal energy remains constant

Question 8

A heat pump delivers $$600\ \mathrm{J} of $$heat to a house for every $$150\ \mathrm{J} of $$work input. What is its coefficient of performance (COP) as a heat pump?

Accepted Answer

$$\mathrm{COP} = 4$$

Question 9

Which process below is most likely to be irreversible?

Accepted Answer

A gas spontaneously expanding into a vacuum

Question 10

A gas is compressed isobarically at $$P = 2\ \mathrm{atm}$$ from $$V_i = 1\ \mathrm{L} to$$ $$V_f = 0.5\ \mathrm{L}. $$How much work is done ON the gas? (1 atm $$= 101.3\ \mathrm{kPa}$$, $$1\ \mathrm{L} = 10$$^{-3}$$\ \mathrm{m}^3)$$

Accepted Answer

$$101.3\ \mathrm{J}$$

Question 11

Which of the following best explains why no heat engine can be 100% efficient?

Accepted Answer

Some energy must always be expelled to the cold reservoir ($$Q_L \u003e 0)$$

Question 12

For a reversible process, the change in entropy is given by which equation?

Accepted Answer

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

Question 13

A heat engine absorbs $$Q_H$$ from a hot reservoir at $$T_H$$ and exhausts $$Q_L to a $$cold reservoir at $$T_L. $$Which equation correctly expresses the energy balance for one cycle?

Accepted Answer

$$Q_H = W + Q_L$$

Question 14

A gas undergoes an isochoric process. Which of the following is true?

Accepted Answer

No work is done ($$W = 0)$$

Question 15

A Carnot engine operating between $$T_H = 600\ \mathrm{K}$$ and $$T_L = 300\ \mathrm{K}$$ absorbs $$1200\ \mathrm{J} of $$heat from the hot reservoir. How much work does it perform per cycle?

Accepted Answer

$$600\ \mathrm{J}$$

Question 16

Which of the following is a correct statement of the Second Law of Thermodynamics?

Accepted Answer

Heat cannot spontaneously flow from a colder body to a hotter body

Question 17

A heat engine receives $$Q_H = 1000\ \mathrm{J}$$ from a hot reservoir and does $$W = 300\ \mathrm{J} of $$work per cycle. How much heat is expelled to the cold reservoir?

Accepted Answer

$$700\ \mathrm{J}$$

Question 18

Which of the following scenarios would result in an increase in the entropy of the universe?

Accepted Answer

A hot object cooling down in a cold room

Question 19

A heat engine operates between $$T_H = 400\ \mathrm{K}$$ and $$T_L = 300\ \mathrm{K}. $$What is the maximum theoretical efficiency?

Accepted Answer

$$e_{max} = 0.25$$

Question 20

Which of the following best describes the direction of natural heat flow according to the Second Law of Thermodynamics?

Accepted Answer

From high temperature to low temperature

Lecture 18

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