The standard heat of formation in $\mathrm{kcal} / \mathrm{mol}$ of $\mathrm{Ba}^{2+}$ is [Given : s

Question

The standard heat of formation in $\mathrm{kcal} / \mathrm{mol}$ of $\mathrm{Ba}^{2+}$ is [Given : standard heat of formation of $\mathrm{SO}_4^{2-}$ ion ${ }_{(a q)}= -216 \mathrm{kcal} / \mathrm{mol}$, standard heat of crystallisation of $\mathrm{BaSO}_{4(s)}=-4.5 \mathrm{kcal} / \mathrm{mol}$, standard heat of formation of $\mathrm{BaSO}_{4(s)}=-349 \mathrm{kcal} / \mathrm{mol}$.

Professor PC Thomas Classes · Answer

(c) :  $\Delta H_f\left(\mathrm{BaSO}_4ight)=\Delta H_f\left(\mathrm{Ba}^{2+}ight)+\Delta H_f\left(\mathrm{SO}_4^{2-}ight) \ +\Delta H_{	ext {crys. }}\left(\mathrm{BaSO}_4ight) \  \Delta H_f\left(\mathrm{Ba}^{2+}ight)= \Delta H_f\left(\mathrm{BaSO}_4ight)-\Delta H_f\left(\mathrm{SO}_4^{2-}ight)-\Delta H_{	ext {crys. }}\left(\mathrm{BaSO}_4ight) \ \Delta H_f\left(\mathrm{Ba}^{2+}ight)= -349+216+4.5 \mathrm{kcal} / \mathrm{mol} \ = -128.5 \mathrm{kcal} / \mathrm{mol}$