For the reaction,$2 H_{2(g)} + O_{2(g)} \longrightarrow 2 H_2 O_{(g)}$,$\Delta H^{\circ} = -573.2 \ kJ$. What is the heat of decomposition of water per mol (in $kJ$)?

Enthalpy change of the reaction $4H_{(g)} \to 2H_{2(g)}$ is $-869.6\, kJ$. The bond dissociation energy of $H-H$ bond is .....$kJ$

The $\Delta_f H^{\circ}$ of $AO_{(s)}$, $BO_{2(g)}$ and $ABO_{3(s)}$ is $-635$, $x$ and $-1210 \ kJ \ mol^{-1}$ respectively.
$ABO_{3(s)} \rightarrow AO_{(s)} + BO_{2(g)} ; \Delta_r H^{\circ} = 175 \ kJ \ mol^{-1}$.
What is the value of $x$ (in $kJ \ mol^{-1}$) ?

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 $N_{2(g)}$.

Enthalpies of formation of $CO_{(g)}$,$CO_{2(g)}$,$N_2O_{(g)}$ and $N_2O_{4(g)}$ are $-110$,$-393$,$81$ and $9.7 \, kJ \, mol^{-1}$ respectively. Find the value of $\Delta_r H$ for the reaction:
$N_2O_{4(g)} + 3 CO_{(g)} \rightarrow N_2O_{(g)} + 3 CO_{2(g)}$

Which substance has a standard molar enthalpy of formation equal to zero at $298 \ K$?