Free Practice Quiz Question List

5 The Second Law and Entropy Online Quiz Questions

Use this free practice quiz with 20 questions to review 5 The Second Law and Entropy, test your knowledge, and prepare for your next test or exam.

20 questions

Written response

1 point

A heat engine absorbs $500\,\mathrm{kJ}$ and rejects $200\,\mathrm{kJ}$ per cycle. What is its thermal efficiency? Enter the value as a percentage.

Written response

1 point

A reversible engine operates between reservoirs at $750\,\mathrm{K}$ and $300\,\mathrm{K}$ . What is its maximum thermal efficiency? Enter a decimal, not a percentage.

Written response

1 point

A heat pump delivers $900\,\mathrm{kJ}$ to a warm region while requiring $300\,\mathrm{kJ}$ of input work. What is its coefficient of performance?

Written response

1 point

A system undergoes a reversible isothermal process at $400\,\mathrm{K}$ and absorbs $1200\,\mathrm{J}$ of heat. What is its entropy change?

Choose one

1 point

Which statement describes the spontaneous direction of heat transfer between two objects at different temperatures?

A
Heat flows spontaneously from a cooler object to a warmer object.
B
Heat flows spontaneously from a warmer object to a cooler object.
C
Heat can flow only when work is supplied.
D
Heat flow always converts all transferred energy into work.

Choose one

1 point

A heat engine absorbs $900\,\mathrm{J}$ from a hot reservoir and rejects $360\,\mathrm{J}$ to a cold reservoir each cycle. How much net work does it produce per cycle?

A
360 J
B
500 J
C
540 J
D
1,260 J

Choose one

1 point

Why can a refrigerator or heat pump have a coefficient of performance greater than 1 without violating energy conservation?

A
A COP can exceed 1 because the device moves heat using supplied work rather than converting work entirely into heat.
B
A COP can exceed 1 only when the device creates energy.
C
A COP is the fraction of input heat converted into work, so it cannot exceed 1.
D
A COP can exceed 1 only if the cold region is warmer than the hot region.

Choose one

1 point

A refrigerator lowers the entropy of its cold interior. Which statement explains how this can be consistent with the second law?

A
No: the entropy of every individual system must always increase.
B
No: the second law requires entropy to remain constant in every process.
C
Yes: any decrease in system entropy is allowed, even if total entropy decreases.
D
Yes: its surroundings can gain at least as much entropy as the system loses, keeping the total entropy change nonnegative.

Choose one

1 point

A system undergoes an irreversible process between two states. How can its entropy change be determined?

A
Use only the heat transferred during the actual irreversible process, divided by the initial temperature.
B
Calculate $\Delta S$ along a reversible path between the same initial and final states.
C
Entropy change cannot be calculated for an irreversible process.
D
Use the work done during the actual process divided by the final temperature.

True or false

1 point

A real heat engine operating between two reservoirs can have an efficiency greater than the Carnot limit for those reservoir temperatures.

A
True
B
False

Choose one

1 point

A heat pump and a refrigerator operate using the same cycle. If the heat-pump coefficient of performance is 4, what is the refrigerator coefficient of performance?

Choose one

1 point

What is the effect of irreversible processes on energy conversion, according to the second law, while still respecting the first law?

A
Energy is conserved, but irreversible entropy generation makes less of it available for conversion into useful work.
B
Energy disappears when entropy is generated, so the first law no longer applies.
C
Irreversibility increases the maximum possible work output by eliminating heat rejection.
D
Entropy generation changes only the amount of energy, not its availability for useful work.

Choose one

1 point

A proposed cyclic engine absorbs heat from a single reservoir and converts all of that heat into work, returning to its initial state after each cycle. Which assessment is correct?

A
The proposal violates the first law because the engine's energy would increase on every cycle.
B
The proposal is ruled out by the second law, even though the energy balance alone may be satisfied.
C
The proposal is possible if the engine operates slowly enough.
D
The proposal is possible as long as the reservoir is sufficiently hot.

Choose all

1 point

Select all statements that accurately describe refrigerators and heat pumps.

A
A refrigerator removes heat from the cold region.
B
A heat pump focuses on delivering heat to the warmer region.
C
For either device, the input work satisfies $W_{in}=Q_H-Q_C$ .
D
A refrigerator and a heat pump move heat from cold to hot without requiring work.
E
A refrigerator's primary useful effect is delivering heat to the warmer region.

Choose all

1 point

Select all statements that correctly distinguish a heat engine from a refrigerator or heat pump.

A
A heat engine absorbs heat from a hot reservoir and rejects some heat to a colder reservoir.
B
A refrigerator uses input work to move heat from a colder region to a warmer one.
C
A refrigerator produces net work by moving heat from cold to hot.
D
A heat pump uses the same kind of cycle as a refrigerator but focuses on delivering heat to the warmer region.
E
A heat engine and a refrigerator both use input work to move heat from cold to hot.

True or false

1 point

True or false: Even if an actual process is irreversible, the entropy change between its initial and final states can be determined using a reversible path connecting those states.

A
True
B
False

True or false

1 point

True or false: A refrigerator and a heat pump both require input work to move heat from a colder region to a warmer region.

A
True
B
False

Fill in the blank

1 point

A device uses input work to keep a food compartment cold by removing heat from it. This device is a .

Fill in the blank

1 point

A building system uses input work to move heat from outdoors into the building and is designed primarily to deliver heat indoors. This device is a .

Open ended

1 point

Explain why a reversible path can be used to determine the entropy change between two states even when the actual process connecting them is irreversible.