THERMODYNAMICS JEE

The enthalpy change for a reaction does not depend upon the

• physical states of reactants and products

• use of different reactants for the same product

• nature of intermediate reaction steps

• difference in initial or final temperatures of involved substances.

The process with negative entropy change is

• dissolution of iodine in water

• sublimation of dry ice

• synthesis of ammonia from N₂ and H₂

• dissociation of CaSO_4(s) to CaO_(s) and SO_3(g)

If an endothermic reaction is non-spontaneous at freezing point of water and becomes feasible at its boiling point, then

• ∆H is –ve, ∆S is +ve

• ∆H and ∆S both are +ve

• ∆H and ∆S both are –ve

• ∆H is +ve, ∆S is –ve

During compression of a spring, the work done is 10 kJ and 2 kJ escaped to the surrounding as heat. The change in internal energy ∆U (in kJ) is

• –8

• 12

• 8

• –12

∆U is equal to

• adiabatic work

• isothermal work

• isochoric work

• isobaric work.

Identify the correct statement regarding a spontaneous process:

• Lowering of energy in the reaction 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.

The standard enthalpy of formation of NH₃ is – 46 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

• – 1102 kJ mol^–1

• – 964 kJ mol^–1

• + 352 kJ mol^–1

• + 1056 kJ mol^–1

A heat engine absorbs heat Q₁ at temperature T₁ and heat Q₂ at temperature T₂. The work done by the engine is J (Q₁ + Q₂). This data

• violates 1^st law of thermodynamics

• violates 1^st law of thermodynamics if Q₁ is –ve

• violates 1^st law of thermodynamics if Q₂ is –ve

• does not violate the 1^st law of thermodynamics.

If the bond dissociation energies of XY, X₂ and Y₂ (all diatomic molecules) are in the ratio of 1: 1: 0.5 and ∆H_f for the formation of XY is –200 kJ mol^–1. The bond dissociation energy of X₂ will be

• 100 kJ mol^–1

• 200 kJ mol^–1

• 800 kJ mol^–1

• 400 kJ mol^–1

(∆H – ∆U) for the formation of carbon monoxide (CO) from its elements at 298 K is (R = 8.314 JK^–1 mol^–1)

• –1238.78 J mol–1

• 1238.78 J mol–1

• –2477.57 J mol–1

• 2477.57 J mol–1