According to second law of thermo-chemistry the law states that the total heat change (ΔH) accompanying a chemical reaction is the same whether the reaction takes place in one or more steps. It means that heat of a reaction depends only on the initial reactants and final products and not on intermediate products that may be formed. Now, ΔH=ΔH1+ΔH2+ΔH3 Enthalpy change in a reaction is always constant and independent of the path followed.