A chemical reaction involves the breaking of bonds in reactants and formation of new bonds in products. The heat of reaction (enthalpy change) depends on the values of the heat needed to break the bonds and heat liberated in the bond formation. Thus (Heat of reaction = Heat needed to break the bonds in reactant – Heat liberated to form bonds in products)

ΔH° = Bond energy in (to break the bonds) x Bond energy out (to form the bonds)

= Bond energy of reactants – Bond energy of products.

A chemical reaction involves the breaking of bonds in reactants and formation of new bonds in products. The heat of reaction (enthalpy change) depends on the values of the heat needed to break the bond formation .Thus (Heat of reaction = (Heat needed to break the bonds in reactants – Heat liberated to from bonds in products).

ΔH^O = Bond energy in (to break the bonds) X Bond energy out (to form the bonds) = Bond energy of reactants – Bond energy of products.