<P> since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns: </P> <Dl> <Dd> 2H (g) + O (g) → 2H O (g) </Dd> <Dd> ΔH = − 483.6 kJ / mol of O </Dd> </Dl> <Dd> 2H (g) + O (g) → 2H O (g) </Dd> <Dd> ΔH = − 483.6 kJ / mol of O </Dd>

Where does energy come from in exothermic reaction