Question

The first ionisation potential of $Na$ is $5.1eV$. The value of electron gain enthalpy of ${Na}^{+}$ will be :

• A. $-10.2eV$
• B. $+2.55eV$
• C. $-2.55eV$
• D. $-5.1eV$

Answer 1

The correct option is D $-5.1eV$

The first ionisation potential of $Na$ is $5.1eV$. The value of electron gain enthalpy of ${Na}^{+}$ will be $-5.1eV$. The reaction is the backward reaction releases the same amount of energy and known as electron gain enthalpy.

$Na\left(g\right)⟶{Na}^{+}\left(g\right)+e;IE=5.1eV$

${Na}^{+}\left(g\right)+e⟶Na\left(g\right);EA=-IE=-5.1eV$.