Thermodynamics · Question 20

In which case change in entropy is negative?

1. Sublimation of solid to gas
2. 2H(g) H2(g)
3. Evaporation of water
4. Expansion of a gas at constant temperature

Under isothermal condition, a gas at 300 K expands from 0.1 L to 0.25 L against a constant external pressure of 2 bar. The work done by the gas is [Given that 1 L bar = 100 J]

1. 25 J
2. 30 J
3. −30 J
4. 5 kJ

The bond dissociation energies of X2, Y2 and XY are in the ratio of 1 : 0.5 : 1. H for the formation of XY is -200 kJ mol-1. The bond dissociation energy of X2 will be

1. 800 kJ mol-1
2. 200 kJ mol-1
3. 400 kJ mol-1
4. 100 kJ mol-1

For a given reaction, H = 35.5 kJ mol-1 and S = 83.6 J K-1 mol-1. The reaction is spontaneous at (Assume that H and S do not vary with temperature.)

1. T > 425 K
2. all temperatures
3. T > 298 K
4. T < 425 K

A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy U of the gas in joules will be

1. -500 J
2. -505 J
3. +505 J
4. 1136.25 J

The correct thermodynamic conditions for the spontaneous reaction at all temperatures is

1. H < 0 and S > 0
2. H < 0 and S < 0
3. H < 0 and S = 0
4. H > 0 and S < 0

For a sample of perfect gas when its pressure is changed isothermally from pi to pf, the entropy change is given by

1. S = nR ( pfpi )
2. S = nR ( pipf )
3. S = nRT ( pfpi )
4. S = RT ( pipf )

The heat of combustion of carbon to CO2 is -393.5 kJ/mol. The heat released upon formation of 35.2 g of CO2 from carbon and oxygen gas is

1. +315 kJ
2. -630 kJ
3. -3.15 kJ
4. -315 kJ

Which of the following statements is correct for a reversible process in a state of equilibrium?

1. G = -2.30 RT K
2. G = 2.30 RT K
3. G = -2.30 RT K
4. G = 2.30 RT K

For the reaction, X2O4(l) 2XO2(g) = 2.1 kcal, S = 20 cal K-1 at 300 K Hence, is

1. 2.7 kcal
2. -2.7 kcal
3. 9.3 kcal
4. -9.3 kcal