From Kirchhoff's equation,which factor affects the heat of reaction?

The enthalpy change for the transition of carbon from diamond to graphite is $\Delta H = -453.5 \ \text{cal}$. What does this indicate?

Enthalpies of formation of $CCl_{4(g)}$,$H_2O_{(g)}$,$CO_{2(g)}$ and $HCl_{(g)}$ are $-105$,$-242$,$-394$ and $-92 \ kJ \ mol^{-1}$ respectively. The magnitude of enthalpy of the reaction given below is $...... \ kJ \ mol^{-1}$ (nearest integer): $CCl_{4(g)} + 2H_2O_{(g)} \rightarrow CO_{2(g)} + 4HCl_{(g)}$

The heats of hydrogenation for $3-$-methylbutene and $2-$-pentene are $-30\, kcal/mol$ and $-28\, kcal/mol$ respectively. The heats of combustion of $2-$-methylbutane and pentane are $-784\, kcal/mol$ and $-782\, kcal/mol$ respectively. All the values are given under standard conditions. Taking into account that combustion of both alkanes gives the same products,what is $\Delta H$ (in $kcal/mol$) for the following reaction under same conditions?
$3-$-methylbutene $\rightleftharpoons$ $2-$-pentene

The bond energy (in $kcal \ mol^{-1}$) of a $C-C$ single bond is approximately:

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