The heat of combustion of methane is $-809 \, kJ \, mol^{-1}$. What is the calorific value of methane in $kJ \, g^{-1}$?

The standard heat of formation,in $kcal / mol$ of $Ba^{2+}$ is
[Given : standard heat of formation of $SO_4^{2-}$ ion $(aq) = -216 \ kcal / mol$,
Standard heat of crystallisation of $BaSO_{4(s)} = -4.5 \ kcal / mol$,standard heat of formation of $BaSO_{4(s)} = -349 \ kcal / mol$]

The standard enthalpy of formation of $CO_{2(g)}$,$CaO_{(s)}$ and $CaCO_{3(s)}$ are $-393, -634, -1210 \ kJ \ mol^{-1}$ respectively. If all the substances are in standard state,the standard enthalpy of decomposition of calcium carbonate to $CaO_{(s)}$ and $CO_{2(g)}$ (in $kJ \ mol^{-1}$) is

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 $kJ \ mol^{-1}$) ?

If the enthalpy of atomisation for $Br_{2(l)}$ is $x \ kJ/mol$ and the bond enthalpy for $Br_{2(g)}$ is $y \ kJ/mol$,what is the relation between them?

Write notes on diatomic molecules and polyatomic molecules with respect to bond dissociation enthalpy.