# 439 Thermodynamic MCQ For All Mechanical Exams

251)The Clausius-Clapeyron equation is given by

1. a) dp/dT = l / T(vf+vi)
2. b) dp/dT = l / T(vf-vi)
3. c) dT/dp = l / T(vf+vi)
4. d) dT/dp = l / T(vf-vi)

Ans-B

252)Water ____ on melting and has the fusion curve with a ____ slope.

1. a) contracts, negative
2. b) contracts, positive
3. c) expands, negative
4. d) expands, positive

Ans-A

253)According to Trouton’s rule, the ratio of latent heat of vaporization to the boiling point at 1.013 bar is

1. a) 77 kJ/kgmol K
2. b) 88 kJ/kgmol K
3. c) 99 kJ/kgmol K
4. d) 100 kJ/kgmol K

Ans-B

254)At the triple point, l(sublimation) = l(vaporization) – l(fusion).

1. a) true
2. b) false

Ans-B

255)The slope of sublimation curve is ____ the slope of the vaporization curve at triple point.

1. a) equal to
2. b) less than
3. c) greater than
4. d) none of the mentioned

Ans-C

256)Latent heat of sublimation is given by

1. a) l(sublimation) = -2.303*(R)*(d(1/T)/d(log p ))
2. b) l(sublimation) = +2.303*(R)*(d(log p )/d(1/T))
3. c) l(sublimation) = +2.303*(R)*(d(1/T)/d(log p ))
4. d) l(sublimation) = -2.303*(R)*(d(log p )/d(1/T))

Ans-D

257) An equation of state can also be used to calculate internal energy, enthalpy and entropy.

1. a) true
2. b) false

Ans-A

258)The changes in properties like T,p and v

1. a) depend on the path taken
2. b) are independent of path
3. c) depends on the property to be evaluated
4. d) none of the mentioned

Ans-B

259)When does an equation of state reduces to the ideal gas equation?

1. a) when the pressure approaches zero
2. b) when the temperature approaches infinity
3. c) both of the mentioned
4. d) none of the mentioned

Ans-C

260)When does the compressibility factor take the value 1?

1. a) for an ideal gas
2. b) when pressure approaches zero
3. c) when temperature approaches infinity
4. d) all of the mentioned

Ans-D

261)For the inversion curve, Joule-Kelvin coefficient is unity.

1. a) true
2. b) false

Ans-B

262)According to the equation of state, the Boyle temperature is

1. a) 2.56*Tc
2. b) 2.50*Tc
3. c) 2.52*Tc
4. d) 2.54*Tc

Ans-D

263)The Gibbs entropy equation is given by

1. a) TdS = dU – pdV – Σ(molal chemical potential)*dn
2. b) TdS = dU + pdV + Σ(molal chemical potential)*dn
3. c) TdS = dU + pdV – Σ(molal chemical potential)*dn
4. d) TdS = dU – pdV + Σ(molal chemical potential)*dn

Ans-C

264)The molal chemical potential is given by

1. a) ∂U/∂S
2. b) ∂U/∂n
3. c) ∂U/∂V
4. d) all of the mentioned

Ans-B

265)The equation written for Gibbs energy can also be written for

1. a) H
2. b) F
3. c) Both of the mentioned
4. d) None of the mentioned

Ans-C

265)Chemical potential is an extensive property.

1. a) true
2. b) false

Ans-B

266)For a phase which has only one constituent,

1. a) chemical potential = n/G
2. b) chemical potential = 1/(G*n)
3. c) chemical potential = G*n
4. d) chemical potential = G/n

Ans-D

267)If a closed system is in equilibrium, which of the following remains constant?

1. a) entropy
2. b) volume
3. c) internal energy
4. d) all of the mentioned

Ans-D

268)At chemical equilibrium, G will be minimum subjected to the equations of constraint.

1. a) true
2. b) false

Ans-A

269)The Gibbs phase rule for a non-reactive system is given by

1. a) f = C + (number of phases) + 2
2. b) f = C – (number of phases) – 2
3. c) f = C – (number of phases) + 2
4. d) f = C – (number of phases) – 2

Ans-C

270)For a pure substance existing in a single phase,

1. a) C=1
2. b) number of phases = 1
3. c) f=2
4. d) all of the mentioned

Ans-D

271)For an isolated system,

1. a) dS<0
2. b) dS>0
3. c) dS=0
4. d) none of the mentioned

Ans-B

272)The entropy of an isolated system always ____ and reaches ____ when equilibrium is reached.

1. a) remains constant, maximum
2. b) decreases, minimum
3. c) increases, maximum
4. d) none of the mentioned

Ans-C

273)Which constraints must be imposed on system to make the Helmholtz function decrease?

1. a) constant T and p
2. b) constant U and T
3. c) constant U and V
4. d) constant T and V

Ans-D

274)If the constraints are constant p and T, then the Gibbs function of a system decreases.

1. a) true
2. b) false

Ans-A

275)A system is said to be in a state of unstable equilibrium when

1. a) dG<0, dF<0, dS<0
2. b) dG<0, dF<0, dS>0
3. c) dG>0, dF>0, dS>0
4. d) dG>0, dF>0, dS<0

Ans-B

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