CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
Two reactions, A and B, both occur at constant pressure.
• Reaction A breaks a small number of very strong bonds and forms a larger number of weak bonds.
• Reaction B breaks several weak bonds and forms a smaller number of very strong bonds.
Which statement about the relative enthalpy changes is most consistent with these descriptions?
(a) Reaction A is more likely exothermic because forming a larger number of bonds releases more energy overall than is absorbed.
(b) Reaction B is more likely endothermic because strong bonds in the products store more energy than weak bonds.
(c) Reaction A is more likely endothermic because the energy absorbed in breaking strong bonds exceeds the energy released when many weak bonds form.
(d) Reaction B is more likely to have ΔH≈0 because the number of bonds broken and formed is similar, so the energy changes nearly cancel out.