At $25^{\circ}C$,the heats of combustion for $CH_{4(g)}$,$C_{(s)}$,and $H_{2(g)}$ are $-212.4 \, kcal$,$-94.0 \, kcal$,and $-68.4 \, kcal$ respectively. The heat of formation for $CH_{4(g)}$ in $kcal$ is:

The enthalpy change of which reaction corresponds to $\Delta H_f^o$ for $Na_2CO_{3(s)}$ at $298 \ K$?

Identify $I, II, III$ in the given Born-Haber cycle diagram for the dissolution of an ionic solid $AB(s)$:
$AB(s) \xrightarrow{I} A^+(aq) + B^-(aq)$
$AB(s) \xrightarrow{II} A^+(g) + B^-(g)$
$A^+(g) + B^-(g) \xrightarrow{III} A^+(aq) + B^-(aq)$

The bond dissociation energies of $X_2$,$Y_2$ and $XY$ are in the ratio of $1 : 0.5 : 1$. $\Delta H$ for the formation of $XY$ is $-200 \ kJ \ mol^{-1}$. The bond dissociation energy of $X_2$ will be $...... \ kJ \ mol^{-1}$.

Which of the following reactions defines the standard enthalpy of combustion,$\Delta H_c^ \circ$?

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:
$N_2O_{4(g)} + 3 CO_{(g)} \rightarrow N_2O_{(g)} + 3 CO_{2(g)}$