The energies of activation for forward and reverse reactions for $\mathrm{A}_{2}+\mathrm{B}_{2}…
The energies of activation for forward and reverse reactions for $\mathrm{A}_{2}+\mathrm{B}_{2} ightleftharpoons 2 \mathrm{AB}$ are $180 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $200 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by $100 \mathrm{k}$. $\mathrm{mol}^{-1} .$ The enthalpy change of the reaction $\left(\mathrm{A}_{2}+\mathrm{B}_{2} ightarrowight.$ $2 \mathrm{AB}$ ) in the presence of a catalyst will be (in $\mathrm{kJ} \mathrm{mol}^{-1}$ ) ______
-20
-15
20
15
Solution
Presence of catalyst does not affect enthalpy change
of reaction $\Delta \mathrm{H}_{\mathrm{R}}=\mathrm{E}_{\mathrm{f}}-\mathrm{E}_{\mathrm{b}}=180-200=-20 \mathrm{~kJ} / \mathrm{mol}$