The bond dissociation energy is the energy required to break a bond in a molecule. In this case, we are given the enthalpy change for the reaction H2 g 2 H g , which is the energy required to break the H-H bond in a diatomic hydrogen molecule.Since the reaction involves breaking one H-H bond, the bond dissociation energy for the H-H bond is equal to the enthalpy change for the reaction.Therefore, the bond dissociation energy for the H-H bond in a diatomic hydrogen molecule is 436 kJ/mol.