question_answer 31)

Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.

Answer:

The second electron gain enthalpy of O is positive, when an electron is added to neutral O atom, a monovalent anion (\[{{O}^{-}}\]) is formed and energy is released, i.e., the first electron gain enthalpy is negative. When second electron is added to form \[{{O}^{2-}}\]anion, there is a lot of electrostatic repulsion as both \[{{O}^{-}}\] anion and electron have negative charge. To overcome force of repulsion, energy is absorbed. Thus, the second electron gain enthalpy of 0 is positive. \[O(g)+e\to {{O}^{-}}(g)\,\,\,\,\,\,\,;\,\,\,\,\,{{\Delta }_{eg}}{{H}_{1}}=-141kJ\,\,mo{{l}^{-1}}\]