Enthalpy is an extensive property. In general, if enthalpy of an overall reaction A→B along one route is Δr H and Δr H1, ΔrH2, Δr H3 ..... represent enthalpies of intermediate reactions leading to product B. What will be the relation between Δr H for overall reaction and Δr H1 , Δr H2 ..... etc. for intermediate reactions.