For $\overline{\mathrm{A}_{2}+\mathrm{B}_{2} \rightleftharpoons 2 \mathrm{AB}}$ $\mathrm{E}_{\mathrm{a}}$ for forward and backward reaction are 180 and $200 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively If catalyst lowers $\mathrm{E}_{\mathrm{a}}$ for both reaction by $100 \mathrm{~kJ} \mathrm{~mol}^{-1}$. Which of the following statement is correct?

(A) Catalyst does not alter the Gibbs energy change of a reaction.

(B) Catalyst can cause non-spontaneous reactions to occur.

(C) The enthalpy change for the reaction is $+20 \mathrm{~kJ} \mathrm{~mol}^{-1}$.

(D) The enthalpy change for the catalysed reaction is different from that of uncatalysed reaction.

JEE Main · 2025 · 04 Apr 2025 · Shift 1 · Chemical Kinetics

For

\overline{A_{2} + B_{2} ⇌ 2 AB}

E_{a}

for forward and backward reaction are 180 and

200 kJ mol^{- 1}

respectively
If catalyst lowers

E_{a}

for both reaction by

100 kJ mol^{- 1}

.
Which of the following statement is correct?

(A)Catalyst does not alter the Gibbs energy change of a reaction.✓ Correct
(B)Catalyst can cause non-spontaneous reactions to occur.
(C)The enthalpy change for the reaction is $+ 20 kJ mol^{- 1}$ .
(D)The enthalpy change for the catalysed reaction is different from that of uncatalysed reaction.

Answer: (A)

Solution

The enthalpy change equals the forward minus the backward activation energy,

Δ H = 180 - 200 = - 20 kJ mo l^{- 1}

, so the reaction is exothermic. A catalyst lowers both activation energies equally and hastens the approach to equilibrium, but it leaves the thermodynamic quantities untouched:

Δ H

, and with it

Δ G

, are the same along the catalysed and uncatalysed paths, and a catalyst can never render a non-spontaneous reaction spontaneous. The correct conclusion is that a catalyst does not alter the Gibbs energy change of the reaction.

JEE Main · 2025 · 04 Apr 2025 · Shift 1 · Single correct option

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JEE Main · 2025 · 04 Apr 2025 · Shift 1 · Chemical Kinetics

Solution

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