The bond dissociation energy of hydrogen gas H2 is the energy required to break the H-H bond in one mole of H2 molecules to form two moles of atomic hydrogen H in the gas phase. It is an important parameter to understand the stability and reactivity of a molecule.The bond dissociation energy of H2 can be calculated using the enthalpy change H of the reaction:H2 g 2H g The enthalpy change of this reaction is equal to the bond dissociation energy, as it represents the energy required to break the H-H bond. For hydrogen gas H2 , the bond dissociation energy is approximately 436 kJ/mol.So, the bond dissociation energy of H2 is 436 kJ/mol, and it can be calculated using the enthalpy change of the given reaction.