# What is the difference between standard enthalpy of combustion and standard enthalpy of formation?

Standard enthalpy change of combustion, or $\Delta {H}_{c}^{\theta}$, is the energy released as heat when a substance undergoes complete combustion at standard temperature and pressure . It is typically measured in ${\text{kJ"*"mol}}^{- 1}$, in which case it may further be regarded as the energy released by 1 mole of the substance.
Standard enthalpy of formation, or $\Delta {H}_{f}^{\theta}$, is the change of enthalpy (so it may be +ive or -ive) when exactly 1 mole of a compound is formed, provided the reactants and products are at standard temperature and pressure.