The first electron gain enthalpy of oxygen is -141 ~kJ ~mol ⁻¹ , its second electron gain enthalpy is:

Step-by-step solution

The first electron gain enthalpy of oxygen is exothermic because energy is released when an electron is added to a neutral oxygen atom to form an O⁻ ion, resulting in a stable configuration. The process is represented as: O(g) + e⁻ O⁻(g) , H = -141 kJ mol ⁻¹ . The second electron gain enthalpy involves adding an electron to a negatively charged O⁻ ion to form an O²⁻ ion: O⁻(g) + e⁻ O²⁻(g) . Since both the incoming electron and the O⁻ ion are negatively charged, there is a strong electrostatic repulsion between them