We have two energy states that the hydrogen molecule possess. When the difference in the energy matches with the supplied energy then one electron is promoted to higher energy level i.e the anti bonding orbital. Putting both the electron in the excited state will require even more energy. When the electron is promoted to the higher energy level then the bond order of the molecule decreases which leads to dissociation. This is in accordance to the observed phenomena that molecules do dissociate when heat is supplied. Solution We have two energy states that the hydrogen molecule possess. When the difference in the energy matches with the supplied energy then one electron is promoted to higher energy level i.e the anti bonding orbital. Putting both the electron in the excited state will require even more energy. When the electron is promoted to the higher energy level then the bond order of the molecule decreases which leads to dissociation. This is in accordance to the observed phenomena that molecules do dissociate when heat is supplied..