Consider the reactions:
$C_{(s)} + 2H_{2(g)} \to CH_{4(g)}, \Delta H = -x \ kcal$
$C_{(g)} + 4H_{(g)} \to CH_{4(g)}, \Delta H = -x_1 \ kcal$
$CH_{4(g)} \to CH_{3(g)} + H_{(g)}, \Delta H = +y \ kcal$
The bond energy of $C-H$ bond is:

$C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)} \dots \dots(I) \quad \Delta H = -393 \, kJ \, mol^{-1}$
$H_{2(g)} + \frac{1}{2} O_{2(g)} \rightarrow H_{2}O_{(l)} \dots \dots(II) \quad \Delta H = -287.3 \, kJ \, mol^{-1}$
$2CO_{2(g)} + 3H_{2}O_{(l)}$ $\rightarrow C_{2}H_{5}OH_{(l)} + 3O_{2(g)} \dots \dots(III) \quad \Delta H = 1366.8 \, kJ \, mol^{-1}$
Find the standard enthalpy of formation of $C_{2}H_{5}OH_{(l)}$.

Enthalpy is an extensive property. In general,if enthalpy of an overall reaction $A \to B$ along one route is $\Delta_r H$ and $\Delta_r H_1, \Delta_r H_2, \Delta_r H_3, \dots$ represent enthalpies of intermediate reactions leading to product $B$. What will be the relation between $\Delta_r H$ for overall reaction and $\Delta_r H_1, \Delta_r H_2, \Delta_r H_3, \dots$ etc. for intermediate reactions?

The heat evolved in the combustion of benzene is given by $C_6H_6 + 7.5 O_2 \to 6CO_2(g) + 3H_2O(l); \Delta H = -3264.6 \, kJ$. Which of the following quantities of heat energy will be evolved when $39 \, g$ of $C_6H_6$ is burnt? (in $kJ$)

The standard enthalpies of combustion of $C_6H_{6(l)}$,$C(graphite)$ and $H_{2(g)}$ are respectively $-3270 \ kJ \ mol^{-1}$,$-394 \ kJ \ mol^{-1}$ and $-286 \ kJ \ mol^{-1}$. What is the standard enthalpy of formation of $C_6H_{6(l)}$ in $kJ \ mol^{-1}$?

The standard heats of combustion of $C_{(s)}$,$S_{(s)}$,and $CS_{2(\ell)}$ are $-393.3 \, kJ \, mol^{-1}$,$-293.72 \, kJ \, mol^{-1}$,and $-1108.76 \, kJ \, mol^{-1}$ respectively. The standard heat of formation of $CS_{2(\ell)}$ in $kJ \, mol^{-1}$ is: