# Entropy And The Second Law Of Thermodynamics - Chapter No 18

Right Answers have been shown below in red color.

1. In a reversible process the system:

A. is always close to equilibrium states
B. is close to equilibrium states only at the beginning and end
C. might never be close to any equilibrium state
D. is close to equilibrium states throughout, except at the beginning and end
E. is none of the above

2. 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

3. The difference in entropy ∆S = SB − SA for two states A and B of a system can be computed as the integral \$ dQ/T provided:

A. A and B are on the same adiabat
B. A and B have the same temperature
C. a reversible path is used for the integral
D. the change in internal energy is first computed
E. the energy absorbed as heat by the system is first computed

4. Possible units of entropy are:

A. J
B. J/K
C. J−1
D. liter·atm
E. cal/mol

5. Which of the following is NOT a state variable?

A. Work
B. Internal energy
C. Entropy
D. Temperature
E. Pressure

6. 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

7. Which of the following processes leads to a change in entropy of zero for the system undergoing the process?

A. Non-cyclic isobaric (constant pressure)
B. Non-cyclic isochoric (constant volume)
C. Non-cyclic isothermal (constant temperature)
D. Any closed cycle
E. None of these

8. 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◦ C to 30◦ C
2. goes from 30◦ C to 40◦ C
3. goes from 40◦ C to 45◦ C
4. goes from 80◦ C to 85◦ 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

9. An ideal gas expands into a vacuum in a rigid vessel. As a result, there are:

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

10. Consider all possible isothermal contractions of an ideal gas. The change in entropy of the gas:

A. is zero for all of them
B. does not decrease for any of them
C. does not increase for any of them
D. increases for all of them
E. decreases for all of them

11. An ideal gas is to taken reversibly from state i, at temperature Tِ1, to any of the other states labeled I, II, III, IV, and V on the p-V diagram below. All are at the same temperature T2. Rank the five processes according to the change in entropy of the gas, least to greatest. A. I, II, III, IV, V
B. V, IV, III, II, I
C. I, then II, III, IV, and V tied
D. I, II, III, and IV tied, then V
E. I and V tied, then II, III, IV

12. An ideal gas, consisting of n moles, undergoes a reversible isothermal process during which the volume changes from Vi to Vf . The change in entropy of the thermal reservoir in contact with the gas is given by:

A. nR(Vf − Vf)
B. nR ln(Vf − Vi)
C. nR ln(Vi / Vf )
D. nR ln(Vf / Vi)
E. none of the above (entropy can’t be calculated for a reversible process)

13. 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. 0
D. RT ln 2
E. 2R

14. An ideal gas, consisting of n moles, undergoes an irreversible process in which the temperature has the same value at the beginning and end. If the volume changes from Vi to Vf , the change in entropy of the gas is given by:

A. nR(Vf − Vi)
B. nR ln(Vf − Vi)
C. nR ln(Vi / Vf )
D. nR ln(Vf / Vi)
E. none of the above (entropy can’t be calculated for an irreversible process)

15. The temperature of n moles of a gas is increased from Ti to Tf at constant volume. If the molar specific heat at constant volume is CV and is independent of temperature, then change in the entropy of the gas is:

A. nCV ln(Tf / Ti)
B. nCV ln(Ti / Tf )
C. nCV ln(Tf − Ti)
D. nCV ln(1 − Ti / Tf )
E. nCV (Tf − Ti)

16. Consider the following processes: The temperature of two identical gases is increased from the same initial temperature to the same final temperature. Reversible processes are used. For gas A the process is carried out at constant volume while for gas B it is carried out at constant pressure. The change in entropy:

A. is the same for A and B
B. is greater for A
C. is greater for B
D. is greater for A only if the initial temperature is low
E. is greater for A only if the initial temperature is high

17. 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 ∆Sh in the entropy of the hot object, the change ∆Sc in the entropy of the cold object, and the change ∆Stotal in the entropy of the combination are:

A. ∆Sh > 0, ∆Sc > 0, ∆Stotal > 0
B. ∆Sh < 0, ∆Sc > 0, ∆Stotal > 0
C. ∆Sh < 0, ∆Sc > 0, ∆Stotal < 0
D. ∆Sh > 0, ∆Sc < 0, ∆Stotal > 0
E. ∆Sh > 0, ∆Sc < 0, ∆Stotal < 0

18. Let SI denote the change in entropy of a sample for an irreversible process from state A to state B. Let SR denote the change in entropy of the same sample for a reversible process from state A to state B. Then:

A. SI > SR
B. SI = SR
C. SI < SR
D. SI = 0
E. SR = 0

19. For all adiabatic processes:

A. the entropy of the system does not change
B. the entropy of the system increases
C. the entropy of the system decreases
D. the entropy of the system does not increase
E. the entropy of the system does not decrease

20. For all reversible processes involving a system and its environment:

A. the entropy of the system does not change
B. the entropy of the system increases
C. the total entropy of the system and its environment does not change
D. the total entropy of the system and its environment increases
E. none of the above