Chemistry - Thermochemistry Question with Solution | TestHub

Enthalpy of combustion refers to 1 mol of the substance burnt completely to the stable products CO₂(g) and H₂O(l). (a) 1 mol ethanol gives CO₂ and liquid water, so it qualifies. (b) burns 2 mol of methanol, so ΔH is twice the molar value. (c) gives water vapour, but the stable form at 298 K is liquid, so ΔH is not the combustion enthalpy of H₂. (d) 1 mol methane gives CO₂(g) and H₂O(l), so it qualifies. Ans (a),(d).