Standard Enthalpy Change of Combustion.

∆H^Θc is the standard enthalpy change when 1 mole of the substance is completely burned in excess oxygen under standard conditions.

Example: C(s) + O2(g) → CO2(g) ∆H^Θ = - x kJmol^-1

If 2C(s) +2O2(g) → 2CO2(g) ∆H^Θ = -2 x kJmol^-1