The heat of formation of $\mathrm{HCl}$ at $348 \mathrm{K}$ from the following data will be:

$\frac{1}{2}{\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to \mathrm{HCl}\left(\mathrm{g}\right); {\mathrm{\Delta }}_{\mathrm{r}}{\mathrm{H}}_{298}=-22060 \mathrm{cal}$

The mean heat capacities over this temperature range are:

${\mathrm{H}}_2\left(\mathrm{g}\right), {\mathrm{C}}_{\mathrm{P}}=6.82 \mathrm{cal} {\mathrm{mol}}^{-1}{\mathrm{K}}^{-1}; {\mathrm{Cl}}_2\left(\mathrm{g}\right), {\mathrm{C}}_{\mathrm{P}}=7.71 \mathrm{cal} {\mathrm{mol}}^{-1}{\mathrm{K}}^{-1};$ $\mathrm{HCl}\left(\mathrm{g}\right), {\mathrm{C}}_{\mathrm{P}}=6.81 \mathrm{cal} {\mathrm{mol}}^{-1}{\mathrm{K}}^{-1}$

Calculate the average $\mathrm{O}-\mathrm{H}$ bond energy in ${\mathrm{H}}_2\mathrm{O}$ with the help of the following data.

$$\begin{gathered} \left(1\right) {\mathrm{H}}_2\mathrm{O}\left(l\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right); ∆{\mathrm{H}}_1=+40.6 \mathrm{kJ} {\mathrm{mol}}^{-1} \\ \left(2\right) 2\mathrm{H}\left(\mathrm{g}\right)\to {\mathrm{H}}_2\left(\mathrm{g}\right); ∆{\mathrm{H}}_2=-435.0 \mathrm{kJ} {\mathrm{mol}}^{-1} \\ \left(3\right) {\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{O}\left(\mathrm{g}\right); ∆{\mathrm{H}}_3=+489.6 \mathrm{kJ} {\mathrm{mol}}^{-1} \\ \left(4\right) 2{\mathrm{H}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(l\right); ∆{\mathrm{H}}_4=-571.6 \mathrm{kJ} {\mathrm{mol}}^{-1} \end{gathered}$$

The average $\mathrm{Xe}-\mathrm{F}$ bond energy is $34 \mathrm{kcal}/\mathrm{mol}$, first I.E. of $\mathrm{Xe}$ is $279 \mathrm{kcal}/\mathrm{mol}$, electron affinity of $\mathrm{F}$ is $85 \mathrm{kcal}/\mathrm{mol}$ and bond dissociation energy of ${\mathrm{F}}_2$ is $38 \mathrm{kcal}/\mathrm{mol}$. Then, the enthalpy change for the reaction

${\mathrm{XeF}}_4\to {\mathrm{Xe}}^{+}+{\mathrm{F}}^{-}+{\mathrm{F}}_2+\mathrm{F}$ will be