Thermodynamics · Question 52

Identify the correct statement for change of Gibbs energy for a system ( Gsystem) at constant temperature and pressure.

1. If Gsystem < 0, the process is not spontaneous.
2. If Gsystem > 0, the process is spontaneous.
3. If Gsystem = 0, the system has attained equilibrium.
4. If Gsystem = 0, the system is still moving in a particular direction.

Assume each reaction is carried out in an open container. For which reaction will H = E?

1. 2CO(g) + O2(g) 2CO2(g)
2. H2(g) + Br2(g) 2HBr(g)
3. C(s) + 2H2O(g) 2H2(g) + CO2(g)
4. PCl5(g) PCl3(g) + Cl2(g)

The enthalpy and entropy change for the reaction: Br2(l) + Cl2(g) 2BrCl(g) are 30 kJ mol-1 and 105 J K-1 mol-1 respectively. The temperature at which the reaction will be in equilibrium is

1. 300 K
2. 285.7 K
3. 273 K
4. 450 K

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