Thermodynamics · Question 55

The enthalpy of hydrogenation of cyclohexene is -119.5 kJ mol-1. If resonance energy of benzene is -150.4 kJ mol-1, its enthalpy of hydrogenation would be

1. -358.5 kJ mol-1
2. -508.9 kJ mol-1
3. -208.1 kJ mol-1
4. -269.9 kJ mol-1

Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction ?

1. Exothermic and increasing disorder
2. Exothermic and decreasing disorder
3. Endothermic and increasing disorder
4. Endothermic and decreasing disorder

A reaction occurs spontaneously if

1. T S < H and both H and S are +ve
2. T S > H and H is +ve and S is −ve
3. T S > H and both H and S are +ve
4. T S = H and both H and S are +ve

The absolute enthalpy of neutralisation of the reaction : MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l) will be

1. -57.33 kJ mol-1
2. greater than -57.33 kJ mol-1
3. less than -57.33 kJ mol-1
4. 57.33 kJ mol-1

If the bond energies of H-H, Br-Br, and H-Br are 433, 192 and 364 kJ mol-1 respectively, the H for the reaction H2(g) + Br2(g) 2HBr(g) is

1. -261 kJ
2. +103 kJ
3. +261 kJ
4. -103 kJ

Standard enthalpy and standard entropy changes for the oxidation of ammonia at 298 K are -382.64 kJ mol-1 and -145.6 J K-1 mol-1, respectively. Standard Gibbs energy change for the same reaction at 298 K is

1. -221.1 kJ mol-1
2. -339.3 kJ mol-1
3. -439.3 kJ mol-1
4. -523.2 kJ mol-1

Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is

1. Ssystem + Ssurroundings > 0
2. Ssystem - Ssurroundings > 0
3. Ssystem > 0 only
4. Ssurroundings > 0 only

The work done during the expansion of a gas from a volume of 4 dm3 to 6 dm3 against a constant external pressure of 3 atm is (1 L atm = 101.32 J)

1. -6 J
2. -608 J
3. +304 J
4. -304 J

For the reaction, C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l) at constant temperature, H - E is

1. +RT
2. -3RT
3. +3RT
4. -RT

The densities of graphite and diamond at 298 K are 2.25 and 3.31 g cm-3, respectively. If the standard free energy difference ( G ) is equal to 1895 J mol-1, the pressure at which graphite will be transformed into diamond at 298 K is

1. 11.14 108 Pa
2. 11.14 107 Pa
3. 11.14 106 Pa
4. 11.14 105 Pa