JEE Main · 2025 · 22 Jan 2025 · Shift 2 · Chemical Kinetics

Reading the reaction-coordinate diagram, the activated complex sits above both reactant and product, with ${\mathrm{E}}_1$ marked as the drop from the activated complex down to the product and ${\mathrm{E}}_2$ as the extra rise of the product above the reactant.

The forward activation energy is the full climb from reactant to the top of the barrier — that is ${\mathrm{E}}_1+{\mathrm{E}}_2$, the barrier height measured from the reactant baseline, not just from the product's.

Since the product lies at higher energy than the reactant, the reaction is endothermic ($\Delta H>0$) and the product is less stable than the reactant; the smaller gap ${\mathrm{E}}_1$, the drop from the top of the barrier down to the product, is what the reverse reaction must climb.

Activation energy of the forward reaction is ${\mathrm{E}}_1+{\mathrm{E}}_2$, and the product is less stable than the reactant.