The bond enthalpies of $H_2$,$X_2$ and $HX$ are in the ratio of $2 : 1 : 2$. If the enthalpy for formation of $HX$ is $-50 \ kJ \ mol^{-1}$,the bond enthalpy of $H_2$ is ..... $kJ \ mol^{-1}$

For the reaction $OF_{2(g)} \to O_{(g)} + 2F_{(g)}$,$\Delta_{rxn}H$ is $368 \ kJ$. What is the average $O-F$ bond energy in $kJ/mol$?

Calculate the heat of formation of $Ca(OH)_{2(s)}$ at $1.8\,^{\circ}C$ from the following data:
$CaO_{(s)} + H_2O_{(l)} \to Ca(OH)_{2(s)}$; $\Delta H_{1.8\,^{\circ}C} = -15.26\,K\,cal$
$H_{2(g)} + \frac{1}{2}O_{2(g)} \to H_2O_{(l)}$; $\Delta H_{1.8\,^{\circ}C} = -68.37\,K\,cal$
$Ca_{(s)} + \frac{1}{2}O_{2(g)} \to CaO_{(s)}$; $\Delta H_{1.8\,^{\circ}C} = -151.80\,K\,cal$

For the reaction $Cu_{(g)}^{+} + I_{(g)}^{-} \to CuI_{(s)}$,the value of $\Delta H^o$ is $-446 \ kJ \ mol^{-1}$. If the ionization energy of $Cu_{(g)}$ is $745 \ kJ \ mol^{-1}$ and the electron affinity of $I_{(g)}$ is $-295 \ kJ \ mol^{-1}$,calculate the value of $\Delta H^o$ for the formation of $CuI_{(s)}$ from $Cu_{(g)}$ and $I_{(g)}$ in $kJ \ mol^{-1}$.

Given the reactions:
$C + \frac{1}{2}O_2 \to CO : \Delta H = -12 \ kJ$
$CO + \frac{1}{2}O_2 \to CO_2 : \Delta H = -10 \ kJ$
For the reaction $C + O_2 \to CO_2 : \Delta H = x \ kJ$,the value of $x$ is: (in $kJ$)

The heat of combustion of carbon is $-94 \ kcal$ at $1 \ atm$ pressure. The internal energy of $CO_2$ is .... $kcal$.