2022 O Level Chem P1 Q16 — Energetics / Activation Energy Solution

Answer: D. Activation energy (\(E_a\)) is the energy hump from reactants to the transition state. For an exothermic reaction, products sit lower than reactants, so the energy released when product bonds form is large — large enough that \(E_a < \text{(energy released forming bonds)}\).

Quantitatively, for any reaction:
energy released forming product bonds = \(E_a +\) (energy gap from peak to products).
In an exothermic reaction the second term is positive, so the energy released forming bonds is strictly greater than \(E_a\). Statement D is correct.

A and C compare \(E_a\) with energy used when bonds form — but bond formation releases energy, not uses it; the comparison is nonsensical. B says \(E_a < \text{released}\) for an endothermic reaction, but in an endothermic reaction the energy gap from peak to products is small, so the inequality doesn't hold reliably. Only D is correct.