Explain standard enthalpy of combustion `(Delta_(c )H^(@))`.

Explanation

It is defined as the enthalpy change accompanying the complete combustion of one mole of a substance in the presence of excess oxygen, provided all the reactants and products are in their standard states.
Example : `C_("(graphite)") + O_(2(g)) rarr CO_(2(g)) " " Delta_(c )H^(@) = -393.5 kJ mol^(-1)`.