Question

From the following identify the change in which electron gain enthalpy is positive. (g = gas phase):

• A. \({Li(g)} \to {Li}^-(g)\)
• B. \({O(g)} \to {O}^-(g)\)
• C. \({Xe(g)} \to {Xe}^-(g)\)
• D. \({S(g)} \to {S}^-(g)\)

Hint:

Noble gases have positive electron gain enthalpy since adding an electron disturbs their stable closed-shell configuration.

Answer 1

The Correct Option is C

Electron gain enthalpy is the energy change when an electron is added to a neutral atom in the gaseous state.
- For most atoms, this process releases energy (negative electron gain enthalpy).
- However, noble gases like Xe have a stable electronic configuration, so adding an electron requires energy input, making the electron gain enthalpy positive.
Hence, electron gain enthalpy is positive for: \[ {Xe(g)} \to {Xe}^-(g) \] Other atoms like Li, O, and S have negative electron gain enthalpy because adding an electron stabilizes them.