Thermodynamics

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

• ΔG = -2.303RT log K

• ΔG = 2.303RT log K

• ΔG⁰ = -2.303RT log K

• ΔG⁰ = -2.303RT log K

A reaction having equal energies of activation for forward and reverse reactions has

• ΔS =0
• ΔG =0
• ΔH = 0
• ΔH = 0

In which of the following reactions, standard reaction entropy changes (ΔS^o) is positive and standard Gibb's energy change (ΔG^o) decreases sharply with increasing temperature?

• C (graphite) +1/2 O₂ (g) → CO (g)

• CO (g) +1/2 (g) → CO₂ (g)

• Mg(s)  +1/2O₂ (g) → MgO (s)

• Mg(s)  +1/2O₂ (g) → MgO (s)

The enthalpy of fusion of water is 1.435 Kcal/mol. The molar entropy change for the melting of ice of at 0^o C is

• 10.52 cal/(mol K)

• 21.04 cal/(mol K)

• 5.260 cal/ (mol K)

• 5.260 cal/ (mol K)

Standard enthalpy of vaporisation Δ_vapH^θ for water for water at 100^oC is 40.66 kJ mol^-1. The internal energy of vaporisation of water at 100^o C (in KJ mol^-1) is

(Assume water vapour to behave like an ideal gas.)

• +37.56

• -43.76

• +43.76

• +43.76

If the enthalpy change for the transition of liquid water to steam is 30kJ mol^-1 at 27^oC, the entropy change for the process would be. 

• 1.0 J mol^- K^-1

• 0.1 J mol^-1 K^-1

• 100 J  mol^-1 K^-1

• 10 J mol^-1 K^-1

Which of the following is the correct option for free expansion of an ideal gas under an adiabatic condition?

Enthalpy change for the reaction,

4H (g) → 2H₂ (g) is - 869.6 kJ

The dissociation energy of H - H bond is

• -869.6 kJ

• +434.8 kJ

• +217.4 kJ

• +217.4 kJ

The heat of combustion of carbon to CO₂ is -395.5 kJ/mol. The heat released upon the formation of 35.2 g CO₂ from carbon and oxygen gas is 

• -315 kJ

• +315 kJ

• -630 kJ

• -630 kJ

The formation of the oxide ion O^2- (g), from oxygen atom requires first an exothermic and then an endothermic step as shown below,


Thus, the process of formation of O^2- in the gas phase is unfavourable even though O^2- is isoelectronic with neon. It is due to the fact that

• electron repulsion outweighs the stability gained by achieving a noble gas configuration

• O^- ion has comparatively smaller size that oxygen atom

• oxygen is more electronegative

• oxygen is more electronegative