The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states.

The reference state of an element is its most stable state of aggregation at 25°C and 1 bar pressure. For example, the reference state of dihydrogen is H₂ gas and those of dioxygen, carbon and sulphur are O₂ gas, Cgraphite and Srhombic respectively.

graphite is thermodynamically most stable allotrope of carbon and, therefore, the enthalpy of formation of graphite is taken as zero.Enthalpy of formation of diamond and fullerene, C60 are 1.90 and 38.1 kJ mol–1, respectively.