Question

What is the value of Electron gain enthalpy of $N{a}^{+}$, if $I{E}_1$ of $Na=5.1eV$ .

• A. $10.2eV$
• B. $-10.2eV$
• C. $-5.1eV$
• D. $5.1eV$

Answer 1

The correct option is C $-5.1eV$

Ionistion enthalpy is defined as the energy required to remove an electron from an isolated gasous atom.
$Na\left(g\right)\to N{a}^{+}\left(g\right)+e^{-}$
Electron gain enthalpy is defined as the enthalpy change when an electron is added to isolated gaseous atom.
$N{a}^{+}\left(g\right)+e^{-}\to Na\left(g\right)$
Therefore, the value of electron gain enthalpy of $N{a}^{+}$ is equal to ionisation enthalpy of $Na$ in magnitude but not sign.