# Thermodynamics Questions and Answers – Reversible Adiabatic Work in a Steady Flow System and Entropy and Disorder

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This set of Thermodynamics Quiz focuses on “Reversible Adiabatic Work in a Steady Flow System and Entropy and Disorder”.

1. The equation W=∫vdp holds good for
a) work-producing machine like an engine or turbine
b) work-absorbing machine like a pump or a compressor
c) both of the mentioned
d) none of the mentioned

Explanation: The equation given here is used for steady flow process and also when the fluid undergoes reversible adiabatic expansion or compression.

2. Only those processes are possible in nature which would give an entropy ____ for the system and the surroundings together.
a) decrease
b) increase
c) remains same
d) none of the mentioned

Explanation: The entropy of an isolated system can never decrease.

3. A process always occurs in such a direction as to cause an increase in the entropy of the universe.
a) true
b) false

Explanation: This comes from the second law which indicates the direction in which a process takes place.
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4. When the potential gradient is ____, the entropy change of the universe is ____
a) large, zero
b) infinitesimal, zero
c) infinitesimal, negative
d) none of the mentioned

Explanation: This makes the process reversible.

5. At equilibrium, the isolated system exists at the peak of the entropy-hill and
a) dS=-1
b) dS=1
c) dS=infinity
d) dS=0

Explanation: At equilibrium, the entropy becomes maximum and hence change in entropy is zero.

6. Which of the following is true?
a) the KE of a gas is due to the coordinated motion of of all the molecules with same average velocity in same direction
b) the PE is due to the displacement of molecules from their normal positions
c) heat energy is due to the random thermal motion of molecules in a disorderly fashion
d) all of the mentioned

Explanation: These are the main causes of Kinetic energy, Potential energy and thermal energy of gas molecules.

7. Orderly energy can be easily converted into disorderly energy.
a) true
b) false

Explanation: An example can be, converting mechanical and electrical energy into internal energy by friction.

8. When work is dissipated into internal energy, what is the change in the disorderly motion of molecules.
a) decreases
b) increases
c) remains same
d) none of the mentioned

Explanation: We know that increase in internal energy causes more random motion.

9. When heat is imparted to a system,
a) the disorderly motion of molecules increases
b) the entropy of the system increases
c) both of the mentioned
d) none of the mentioned

Explanation: As heat is given to a system, its internal energy increases, thus increasing the entropy of the system.

10. Which of the following relation is correct?
a) S=lnK/W
b) S=K/lnW
c) S=lnK*W
d) S=K*lnW

Explanation: S=K*lnW where S is the entropy, W is the thermodynamic probability, and K is the Boltzmann constant.

11. In the reversible adiabatic expansion of a gas the increase in disorder due to an increase in volume is compensated by the decrease in disorder due to a decrease in temperature.
a) true
b) false

Explanation: This ensures that the disorder number or entropy remains constant.

12. When does the entropy of a system become zero?
a) W=0
b) W=1
c) W=-1
d) none of the mentioned

Explanation: When thermodynamic probablity W=1, we get S=0 from S=K*lnW and this happens only at T=0K.

13. According to the Boltzmann,
a) he introduced the thermodynamic probability with each state
b) increase in entropy implies that the system proceeds by itself towards a state of higher thermodynamic probability
c) an irreversible process goes on happening until the most probable is achieved
d) all of the mentioned

Explanation: This is how Boltzmann introduced statistical concepts to define disorder.

14. When W=1, we get S=0 which can occur only at T=0K. This is the Nernst-Simon statement of third law of thermodynamics.
a) true
b) false

Explanation: But the state of T=0K cannot be reached in a finite number of operations.

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