question_answer

               Given that (i) \[O\,(g)+{{e}^{-}}\xrightarrow{\,}\,{{O}^{-}}(g),\]\[\Delta H=-142\,kJ\,mo{{l}^{-1}}\] (ii)\[O(g)+2\,{{e}^{-}}\xrightarrow{\,}\,{{O}^{2-}}(g),\] \[\,\Delta H=+712\,kJ\,mo{{l}^{-1}}\]  Calculate \[\,\Delta H\] for the reaction \[{{O}^{-}}(g)+{{e}^{-}}\xrightarrow{\,}\,{{O}^{2-}}(g)\].

Answer:

                Eqn. (ii) - Eqn. (i) gives \[{{O}^{-}}(g)+{{e}^{-}}\,\xrightarrow{\,}\,{{O}^{2-}},\]\[\Delta H=712\,-(-142)kJ\,mo{{l}^{-1}}=854\,kJ\,mo{{l}^{-1}}\].