Ionization enthalpy of an atom is equal to : — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Consider the forward ionization reaction of a gaseous atom X: X(g) -> X^+(g) + e^-. The enthalpy change for this process is defined as the ionization enthalpy of X. Step 2: Consider the reverse process where the gaseous cation gains an electron: X^+(g) + e^- -> X(g). The enthalpy change for this process is defined as the electron gain enthalpy of the cation X^+. Step 3: Since the reverse reaction is the exact opposite of the forward reaction, their enthalpy changes are equal in magnitude (though opposite in sign), making the ionization enthalpy of X equal in magnitude to the electron gain enthalpy of the cation X^+.