The formation of the oxide ion" O-2(g) " requires first an exothermic and then an endothermic step as shown below ;O(g) + e– → O–(g);    ΔH0 = – 142kJmol–1  ; O–(g) + e– → O(g)-2;  ΔH0 = 844 kJmol–1. This is because