• # 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.

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. $O(g)+e\to {{O}^{-}}(g)\,\,\,\,\,\,\,;\,\,\,\,\,{{\Delta }_{eg}}{{H}_{1}}=-141kJ\,\,mo{{l}^{-1}}$