2021 O Level Chem P1 Q14 — Energetics / Bond Energies Solution

Answer: D. Burning methane is exothermic, so the products lie at a lower energy than the reactants. On the energy profile, x is the energy absorbed to break the reactant bonds (the climb up to the peak) and z is the energy released when the product bonds form (the drop down to the products).

For any exothermic reaction the energy released in forming bonds is greater than the energy absorbed in breaking bonds — that is why energy is given out overall (\(z > x\)).

So the correct statement is: the energy released in forming bonds is more than the energy absorbed in breaking bonds. Statements that reverse this, or claim the two are equal, describe endothermic or thermoneutral reactions instead.