# Thermodynamics Questions and Answers – First and Second Laws Combined

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This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “First and Second Laws Combined”.

1. The equation TdS=dU+pdV is obtained from which law?
a) first law
b) second law
c) both of the mentioned
d) none of the mentioned

Explanation: By first law, dQ=dU+pdV and from second law, dQ=TdS.

2. Which of the following equation is true?
a) TdS=dH+Vdp
b) TdS=dH-Vdp
c) TdS=-dH-Vdp
d) TdS=-dH+Vdp

Explanation: It comes from TdS=dU+pdV and H=U+pV.

3. The equation dQ=dE+dW holds good for
a) any process, reversible or irreversible
b) only reversible process
c) only irreversible process
d) none of the mentioned

Explanation: This equation holds good for any process and for any system.
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4. The equation dQ=dU+pdW holds good for any process undergone by a closed stationary system.
a) true
b) false

Explanation: When a closed stationary system undergoes a process, this equation holds true.

5. The equation dQ=dU+pdV holds good for
a) open system
b) closed system
c) both of the mentioned
d) none of the mentioned

Explanation: This equation is true only for a reversible(quasi-static) process.

6. The equation TdS=dU+pdV holds good for
a) reversible process
b) reversible process
c) both of the mentioned
d) none of the mentioned

Explanation: This equation holds good for any process undergone by a closed system since it is a relation among properties which are independent of the path.

7. The equation dQ=TdS is true only for a reversible process.
a) true
b) false

Explanation: This comes from the second law.

8. The equation TdS=dH-Vdp
a) relates only the properties of a system
b) there is no path function term in the equation
c) the equation holds good for any process
d) all of the mentioned

Explanation: Since there is no path function in the equation hence the equation holds good for any process.

9. The entropy change of a system between two identifiable equilibrium state is ___ when the intervening process is reversible or change of state is irreversible.
a) different
b) same
c) depends on the process
d) none of the mentioned

Explanation: To determine the change in entropy, a known reversible path is made to connect the two end states and integration is performed on this path.

10. It is better to state that “the change of state is irreversible, rather than say it is an irreversible process”.
a) true
b) false

Explanation: This is because no irreversible path or process can be plotted on thermodynamic coordinates.

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