Hess's law of constant heat summation is based on

From the following data:
$CH_3OH_{(l)} + \frac{3}{2}O_{2(g)} \longrightarrow CO_{2(g)} + 2H_2O_{(l)}$; $\Delta_rH^{\circ} = -726 \ kJ \ mol^{-1}$
$H_{2(g)} + \frac{1}{2}O_{2(g)} \longrightarrow H_2O_{(l)}$; $\Delta_rH^{\circ} = -286 \ kJ \ mol^{-1}$
$C_{(graphite)} + O_{2(g)} \longrightarrow CO_{2(g)}$; $\Delta_rH^{\circ} = -393 \ kJ \ mol^{-1}$
The standard enthalpy of formation of $CH_3OH_{(l)}$ in $kJ \ mol^{-1}$ is:

The standard heats of formation in $kcal \ mol^{-1}$ of $NO_{2(g)}$ and $N_2O_{4(g)}$ are $8.0$ and $2.0$ respectively. The heat of dimerization of $NO_2$ in $kcal$ for the reaction $2NO_{2(g)} \rightarrow N_2O_{4(g)}$ is:

Standard enthalpy of formation of water is $-286 \ kJ \ mol^{-1}$. When $1800 \ mg$ of water is formed from its constituent elements in their standard states,the amount of energy liberated is: (in $kJ$)

Given that bond energies of $H-H$ and $Cl-Cl$ are $430 \ kJ \ mol^{-1}$ and $240 \ kJ \ mol^{-1}$ respectively and $\Delta H_f$ for $HCl$ is $-90 \ kJ \ mol^{-1},$ the bond enthalpy of $HCl$ is ............... $kJ \ mol^{-1}$.

The standard enthalpy of combustion at $25\,^{\circ}C$ of hydrogen,cyclohexene $(C_6H_{10})$ and cyclohexane $(C_6H_{12})$ are $-241$,$-3800$ and $-3920\, kJ/mol$ respectively. Calculate the heat of hydrogenation of cyclohexene in $kJ/mol$.