The formulation of F (g) from F (g) is exothermic whereas that of O2- (g) from O (g) is endothermic. Explain.
F (g) + e– (g) → F (g); ΔH = Negative Energy is released when an extra electron from outside is added to a neutral isolated gaseous atom of an element. To convert, O (g) to O2- (g) two steps are required (i) O (g) + e– (g) → O– (g); ΔH1 = – 141 kJ mol-1 (ii) O– (g) + e– (g) → O2- (g); ΔH2 = + 780 kJ mol-1 Hence the over all processes endothermic (+ 780 – 141 = + 639 kJ mol-1) whereas F (g) to F– (g) is exothermic.
