Calculate the net energy released or absorbed in converting 1 gm of oxygen atoms into O2- ions

1. The reactions and the respective Electron Affinities are as follows :

         (a) O(g) + e^- $\to$O^-(g)                   E_a = -142 kJ/mol
Energy is released because of high electronegativity of Oxygen.

      (b) O^-(g) + e^- $\to$O^2-(g)                   E_a = + 844 kJ/mol
Energy is absorbed as an electron is forcibly pushed into a negatively charged ion.

2. Net E_a = -142 + 844 = 702 kJ/mol,that is energy is absorbed.