Question

The enthalpy of neutralization of a weak acid in 1 M solution with a strong base is $–56.1kJmo{l}^{-1}$. The enthalpy of ionization of the acid is $YkJmo{l}^{-1}$ and enthalpy of neutralization of the strong acid with a strong base is $-57.3kJequi{v}^{-1}$, if the $\%$ ionization of the weak acid in molar solution is $20\%$ (assume the acid to be monobasic), then what is value of Y?

Answer 1

$\begin{array}{ccccc}HA& \rightleftharpoons & H^{+}& +& A^{-}\\ 1-\alpha & & \alpha & & \alpha \end{array}$
Only $1-\alpha$ mol needs to ionize
So, $-56.1=-57.3+(1-\alpha )Y$
$\Rightarrow -56.1=-57.3+(1-0.2)Y$
$\Rightarrow Y=1.5kJ/mol$