Solution

The standard enthalpy of formation of NH₃ is – 46.0 kJ mol^-1.If the enthalpy of formation of H₂ from its atoms is– 436 kJ mol^-1 and that of N₂ is – 712 kJ mol^-1, the average bond enthalpy of N – H bond in NH₃ is

– 964 kJ mol^-1
+ 352 kJ mol^-1
+ 1056 kJ mol^-1
– 1102 kJ mol^-1

Solution

Identify the correct statement regarding a spontaneous process

Lowering of energy in the process is the only criterion for spontaneity.
For a spontaneous process in an isolated system, the change in entropy is positive
Endothermic processes are never spontaneous.
Exothermic processes are always spontaneous.

Solution

Spontaneity of reaction depends on tendency to acquire minimum energy state and maximum randomness. For a spontaneous process in an isolated system the change in entropy is positive.

Equal volumes of two monoatomic gases, A and B, at same temperature and pressure are mixed. The ratio of specific heats (C_p/C_v) of the mixture will be :

0.83
1.50
3.3
1.67

Solution

The enthalpy of fusion of water is 1.435 kcal/mol.The molar entropy change for the melting of ice at 0°C is :

10.52 cal /(mol K)
21.04 cal / (mol K)
5.260 cal / (mol K)
0.526 cal / (mol K)

Solution

Enthalpy change for the reaction, 4H(g) ⟶ 2H₂(g) is – 869.6 kJ.
The dissociation energy of H–H bond is :

– 434.8 kJ
– 869.6 kJ
+ 434.8 kJ
+ 217.4 kJ

Solution

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

10 J mol^-1 K^-1
1.0 J mol^-1 K^-1
0.1 J mol^-1 K^-1
100 J mol^-1 K^-1

Solution

Three moles of an ideal gas expanded spontaneously into vacuum. The work done will be :

Zero
Infinite
3 Joules
9 Joules

Solution

Ideal gas during spontaneous expansion into vacuum does not do any external work.

Solution

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