When the first electron gain enthalpy (∆egH) of oxygen is -141 kJ/mol, its second electron gain enthalpy is:
When the first electron gain enthalpy (∆egH) of oxygen is -141 kJ/mol, its second electron gain enthalpy is: Correct Answer A positive value
Concept:
The second electron gain enthalpy of oxygen is positive as energy has to be added for the addition of another electron.
Electron gain enthalpy is defined as the amount of energy released when an electron is added to an isolated gaseous atom. During the addition of an electron, energy can either be released or absorbed. Sign convention for electron gain enthalpy negative when energy is released while accepting an electron.
As the first electron gain enthalpy of oxygen can be shown as,
O(g) + e- → O-(g) ∆egH1 = -141 kJ/mol
This expression of second electron gain enthalpy of oxygen will be,
O- (g) + e- → O2- (g), ∆egH2 = + ve
∆egH2 of oxygen is positive, that is endothermic because a strong electrostatic repulsion will be observed between highly negative O- and the incoming electron e-. A very high amount of energy will be consumed by the system to overcome the electrostatic repulsion.