Given the reactions:
$C + \frac{1}{2}O_2 \to CO : \Delta H = -12 \ kJ$
$CO + \frac{1}{2}O_2 \to CO_2 : \Delta H = -10 \ kJ$
For the reaction $C + O_2 \to CO_2 : \Delta H = x \ kJ$,the value of $x$ is: (in $kJ$)

At $25^{\circ} \text{C}$, the standard enthalpies of combustion of $H_2(g)$, cyclohexene $(C_6H_{10})$, and cyclohexane $(C_6H_{12})$ are $-241 \text{ kJ mol}^{-1}$, $-3800 \text{ kJ mol}^{-1}$, and $-3920 \text{ kJ mol}^{-1}$ respectively. Calculate the heat of hydrogenation of cyclohexene.

When $2 \ mol$ of $C_2H_{6(g)}$ is completely combusted,it releases $3129 \ kJ$ of heat. What is the enthalpy of formation of $C_2H_{6(g)}$? The $\Delta H_f$ values for $CO_{2(g)}$ and $H_2O_{(l)}$ are $-395 \ kJ \ mol^{-1}$ and $-286 \ kJ \ mol^{-1}$ respectively.

Calculate the enthalpy of formation of ethylene $(C_2H_4)$ from the following data:
$I. C_{(graphite)} + O_{2(g)} \rightarrow CO_{2(g)}; \Delta H = -393.5 \ kJ$
$II. H_{2(g)} + \frac{1}{2}O_{2(g)} \rightarrow H_2O_{(l)}; \Delta H = -286.2 \ kJ$
$III. C_2H_{4(g)} + 3O_{2(g)} \rightarrow 2CO_{2(g)} + 2H_2O_{(l)}; \Delta H = -1410.8 \ kJ$ (in $kJ$)

Which of the following equations correctly represents the standard heat of formation $(\Delta H_f^o)$ of methane?

The heat change for the reaction $H_2 + \frac{1}{2} O_2 \to H_2 O$ is called