CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
For complete combustion of two different fuels, the following data are available.
Reaction 1: H₂(g) + ½ O₂(g) → H₂O(l) ΔH° = −285.8 kJ mol⁻¹
Reaction 2: CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(l) ΔH° = −890.3 kJ mol⁻¹
Which statement best explains why Reaction 1 releases more energy per gram of fuel than Reaction 2?
(a) Because CH₄ releases a larger ΔH∘ per mole of fuel, it must also release more energy per gram.
(b) H₂ has a much lower molar mass, so fewer grams correspond to each mole of energy released.
(c) Combustion of H₂ consumes less O2, making the process inherently more exothermic.
(d) H₂ forms stronger O–H bonds than CH₄ forms C–H bonds during combustion.