Hess's law of constant heat summation includes:

What is the standard $N \equiv N$ bond enthalpy from the following reaction? $N_{2(g)} + 3H_{2(g)} \longrightarrow 2NH_{3(g)} \quad \Delta H^{\circ} = -83 \ kJ$
Given: $(\Delta H^{\circ}_{(H-H)} = 435 \ kJ \text{ mol}^{-1}, \Delta H^{\circ}_{(N-H)} = 389 \ kJ \text{ mol}^{-1})$

Calculate the standard enthalpy change of the following reaction: $CH_{4(g)} + 2O_{2(g)} \rightarrow CO_{2(g)} + 2H_{2}O_{(\ell)}$ if $\Delta_{f} H^{\circ}(CH_{4}) = -75 \ kJ \ mol^{-1}$,$\Delta_{f} H^{\circ}(CO_{2}) = -390 \ kJ \ mol^{-1}$,and $\Delta_{f} H^{\circ}(H_{2}O) = -286 \ kJ \ mol^{-1}$.

How much heat in $kJ$ is produced by the combustion of $15.5 \, g$ of propane? ${C_3H_8} + 5{O_2} \to 3{CO_2} + 4{H_2O}; \Delta{H^o} = -2219 \, kJ/mol$

The standard enthalpy of formation of $H_2O_{(g)}$ at $298 \ K$ is $-241.82 \ kJ \ mol^{-1}$. Calculate the enthalpy of formation of $H_2O_{(g)}$ at $373 \ K$,assuming $C_p$ is independent of temperature.
$C_p$ of $H_2O_{(g)} = 33.58 \ J \ K^{-1} \ mol^{-1}$
$C_p$ of $H_{2(g)} = 28.84 \ J \ K^{-1} \ mol^{-1}$
$C_p$ of $O_{2(g)} = 29.37 \ J \ K^{-1} \ mol^{-1}$

Find the value $\Delta H_f^o[NH_{3(g)}]$ if $\Delta H_r$ for the reaction $N_{2(g)} + 3H_{2(g)} \to 2NH_{3(g)}$ is $-\,183.6 \ kJ/mol$ of $N_{2(g)}$.