Question

Account for the following : 
Although Fluorine has less negative electron gain enthalpy yet F₂ is a strong oxidizing agent.

Answer 1

The oxidizing capability of a substance depends upon three factors: bond dissociation enthalpy, electron gain enthalpy, and hydration energy.
Although electron gain enthalpy of fluorine is less negative as compared to chlorine, fluorine is a stronger oxidizing agent than chlorine, because of low enthalpy of dissociation of F-F bond (158.8/ kJ mol^-1) and high hydration enthalpy of F^- (515/ kJ mol^-1).
Due to its small size, Fluorine's hydration energy is very high hence better the oxidizing power. Fluorine has a greater electron-electron repulsion among the lone pairs in the small-sized F₂ molecule where they are much closer to each other than in the case of Cl₂, hence the enthalpy of dissociation of F₂ is lower than Cl₂ which makes it better oxidizing agent.