Thermodynamics Questions and Answers – Types of Equilibrium

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

1. For an isolated system,
a) dS<0
b) dS>0
c) dS=0
d) none of the mentioned
View Answer

Answer: b
Explanation: We have dU+pdV-TdS<0 and for isolated system, U and V are constant.
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2. The entropy of an isolated system always ____ and reaches ____ when equilibrium is reached.
a) remains constant, maximum
b) decreases, minimum
c) increases, maximum
d) none of the mentioned
View Answer

Answer: c
Explanation: This is because dS>0 for an isolated system.

3. Which constraints must be imposed on system to make the Helmholtz function decrease?
a) constant T and p
b) constant U and T
c) constant U and V
d) constant T and V
View Answer

Answer: d
Explanation: In these constraints, the Helmholtz function decreases and becomes minimum at final equilibrium state.
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4. If the constraints are constant p and T, then the Gibbs function of a system decreases.
a) true
b) false
View Answer

Answer: a
Explanation: The Gibbs function becomes minimum at the final equilibrium state.

5. Which of the following statement is true?
a) a system is in equilibrium state if, when it is disturbed, it comes back to its original state
b) if there is a spontaneous change in the state, the system is not in equilibrium
c) during a spontaneous change, the entropy of system increases
d) all of the mentioned
View Answer

Answer: d
Explanation: During a spontaneous change, the entropy of system increases and reaches a maximum when equilibrium is reached.
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6. A system is said to be in a state of unstable equilibrium when
a) dG<0, dF<0, dS<0
b) dG<0, dF<0, dS>0
c) dG>0, dF>0, dS>0
d) dG>0, dF>0, dS<0
View Answer

Answer: b
Explanation: These conditions refer to a spontaneous change which makes unstable equilibrium.

7. What is the criterion of stability?
a) dG<0, dF<0, dS<0
b) dG<0, dF<0, dS>0
c) dG>0, dF>0, dS>0
d) dG>0, dF>0, dS<0
View Answer

Answer: d
Explanation: For these conditions, a system is said to be in a state of stable equilibrium.
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8. For a system to be in a state of neutral equilibrium,
a) dS=dG=dF=0
b) dS=0, dG=dF<0
c) dS=0, dG=dF>0
d) none of the mentioned
View Answer

Answer: a
Explanation: The thermodynamic criterion of equilibrium thus remains at constant value for all possible variations.

9. If a system is stable to small but not large disturbances, it is said to be in metastable equilibrium.
a) true
b) false
View Answer

Answer: a
Explanation: This is the definition of metastable equilibrium and an example can be mixture of oxygen and hygrogen.
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10. Which of the following is true for a system at equilibrium?
a) S=Smax and ∂S=0
b) F=Fmin and ∂F=0
c) G=Gmin and ∂G=0
d) all of the mentioned
View Answer

Answer: d
Explanation: These are necessary but not the sufficient conditions for equilibrium.

11. For thermal stability,
a) Cv>0
b) (∂p/∂V)<0, at constant entropy
c) both of the mentioned
d) none of the mentioned
View Answer

Answer: a
Explanation: Since T>0K , Cv>0 for thermal stability.

12. For mechanical stability,
a) Cv>0
b) (∂p/∂V)<0, at constant entropy
c) (∂p/∂V)<0, at constant temperature
d) all of the mentioned
View Answer

Answer: c
Explanation: This is the condition for mechanical stability.

13. For total stability,
a) Cv>0
b) (∂p/∂V)<0, at constant entropy
c) (∂p/∂V)<0, at constant temperature
d) all of the mentioned
View Answer

Answer: d
Explanation: All these three conditions are required for stability.

14. The third law is a fundamental law of nature and cannot be proved.
a) true
b) false
View Answer

Answer: a
Explanation: The third law is not derivable from second law and cannot be proved as is the case with zeroth, first and second laws.

15. For magnetic cooling, ____ salt is used.
a) diamagnetic
b) paramagnetic
c) both of the mentioned
d) none of the mentioned
View Answer

Answer: b
Explanation: A paramagnetic salt like gadolinium sulphate is used for magnetic cooling.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter