q = C × ΔT; ΔHc = q / n
The heat of combustion (ΔHc) is the enthalpy change when one mole of a substance burns completely in oxygen. It is measured using a bomb calorimeter — a sealed, constant-volume device where the sample is ignited electrically. The heat released raises the temperature of the calorimeter: q = C × ΔT, where C is the calorimeter's heat capacity. Dividing by the sample mass gives kJ/g; multiplying by molar mass gives kJ/mol. Typical values: hydrogen −286 kJ/mol, methane −890, ethanol −1367, glucose −2803. Food calories are determined by bomb calorimetry (1 food Cal = 4.184 kJ). Heat of combustion is crucial in fuel science, nutrition labeling, and thermochemical calculations using Hess's law.