Deck 5: Entropy and the Second Law of Thermodynamics

Question 1

A slow (quasi-static) process is NOT reversible if:

A) the temperature changes
B) energy is absorbed or emitted as heat
C) work is done on the system
D) friction is present
E) the pressure changes

Answer 1

friction is present

Question 2

The change in entropy is zero for:

A) reversible adiabatic processes
B) reversible isothermal processes
C) reversible processes during which no work is done
D) reversible isobaric processes
E) all adiabatic processes

Answer 2

reversible adiabatic processes

Question 3

Rank from smallest to largest, the changes in entropy of a pan of water on a hot plate, as the temperature of the water
1) goes from 20 $\degree$ to 30 $\degree$ C
2) goes from 30 $\degree$ to 40 $\degree$ C.
3) goes from 40 $\degree$ to 45 $\degree$ C
4) foes from 80 $\degree$ to 85 $\degree$ C

A) 1, 2, 3, 4
B) 4, 3, 2, 1
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.

Answer 3

4, 3, 2, 1.

Question 4

An ideal gas expands into a vacuum in a rigid vessel. As a result there is:

A) a change in entropy
B) an increase of pressure
C) a change in temperature
D) a decrease of internal energy
E) a change in phase

Question 5

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

Question 6

A hot object and a cold object are placed in thermal contact and the combination is isolated. They transfer energy until they reach a common temperature. The change $\Delta$ S_h in the entropy of the hot object, the change $\Delta$ S_c in the entropy of the cold object, and the change $\Delta$ S_total in the entropy of the combination are:

A) $\Delta$ S_h > 0, $\Delta$ S_c > 0, $\Delta$ S_total > 0
B) $\Delta$ S_h < 0, $\Delta$ S_c > 0, $\Delta$ S_total > 0
C) $\Delta$ S_h < 0, $\Delta$ S_c > 0, $\Delta$ S_total < 0
D) $\Delta$ S_h > 0, $\Delta$ S_c < 0, $\Delta$ S_total > 0
E) $\Delta$ S_h > 0, $\Delta$ S_c < 0, $\Delta$ S_total < 0

Question 7

For all adiabatic processes:

A) the entropy does not change
B) the entropy increases
C) the entropy decreases
D) the entropy does not increase
E) the entropy does not decrease

Question 8

A Carnot cycle heat engine operates between 400 K and 500 K. Its efficiency is:

A) 20%
B) 25%
C) 44%
D) 79%
E) 100%

Question 9

The maximum theoretical efficiency of a Carnot engine operating between reservoirs at the steam point and at room temperature is about:

A) 10%
B) 20%
C) 50%
D) 80%
E) 99%

Question 10

Consider the following processes:
I. Energy flows as heat from a hot object to a colder object
II.Work is done on a system and an equivalent amount of energy is
Rejected as heat by the system
III. Energy is absorbed as heat by a system and an equivalent amount
Of work is done by the system
Which are never found to occur?

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