JEE MAIN - Chemistry (2025 - 4th April Morning Shift - No. 1)

For $\mathrm{A}_2+\mathrm{B}_2 \rightleftharpoons 2 \mathrm{AB}$

$\mathrm{E}_{\mathrm{a}}$ 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?

Catalyst does not alter the Gibbs energy change of a reaction.
The enthalpy change for the reaction is $+20 \mathrm{~kJ} \mathrm{~mol}^{-1}$.
Catalyst can cause non-spontaneous reactions to occur.
The enthalpy change for the catalysed reaction is different from that of uncatalysed reaction.

Explanation

$\mathrm{A}_2+\mathrm{B}_2 \rightleftharpoons 2 \mathrm{AB}$

$$\begin{aligned} &\begin{aligned} & \mathrm{E}_{\mathrm{f}}=180 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \mathrm{E}_{\mathrm{b}}=200 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \Delta \mathrm{H}=\mathrm{E}_{\mathrm{f}}-\mathrm{E}_{\mathrm{b}}=-20 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}\\ &\text { In presence of catalyst : }\\ &\begin{aligned} & \mathrm{E}_{\mathrm{f}}=180-100=80 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \mathrm{E}_{\mathrm{b}}=200-100=100 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned} \end{aligned}$$

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