# Thermodynamics Questions and Answers – Useful Work

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Useful Work”.

1. Useful work is given by
a) actual work + p(V2-V1)
b) actual work – p(V2-V1)
c) actual work + p(V2+V1)
d) none of the mentioned

Explanation: Useful work = actual work – work performed on the atmosphere.

2. In a steady flow system, which of the following does not change?
a) mass
b) volume
c) both of the mentioned
d) none of the mentioned

Explanation: The volume of the system remains constant for a steady flow system.

3. Which of the following is true?
a) in a steady flow system, no work is done on the atmosphere
b) in case of unsteady flow system, the volume of the system changes
c) both of the mentioned
d) none of the mentioned

Explanation: In a steady flow system, the volume of the system does not change but it changes for unsteady flow system.

4. Availability function for a closed system is given by
a) U-pV+TS
b) U+pV+TS
c) U-pV-TS
d) U+pV-TS

Explanation: This term comes very frequent and is considered as availability function.

5. When a system exchanges heat with a thermal energy reservoir in addition to the atmosphere, the maximum useful work
a) increases
b) decreases
c) remains constant
d) none of the mentioned

Explanation: The maximum useful work increases in this case.

6. When the system is in equilibrium with the surroundings, this state of the system is known as dead state.
a) true
b) false

Explanation: In this state, the system has pressure and temperature as that of surroundings, there is no chemical reaction mass transfer and has minimum potential energy.

7. When a system exchanges heat with a thermal energy reservoir at temperature Tr in addition to the atmosphere, the maximum useful work increases by
a) dQ(1+Tr/To)
b) dQ(1-Tr/To)
c) dQ(1+To/Tr)
d) dQ(1-To/Tr)

Explanation: The maximum useful work will be increased by dQ(1-To/Tr) where dQ is the heat received by the system.

8. When a system changes its state towards that of surroundings, the opportunity to produce more work
a) increases
b) decreases
c) remains constant
d) none of the mentioned

Explanation: More the system goes towards surroundings, lesser is the opportunity to produce more work.

9. When the system is in equilibrium with the surroundings, it must be in
a) pressure equilibrium
b) temperature equilibrium
c) chemical equilibrium
d) all of the mentioned

Explanation: When the system is in equilibrium with the surroundings, its pressure and temperature is Po and To and there should not be any chemical reaction or mass transfer.

10. All spontaneous processes terminate at the dead state.
a) true
b) false