The enthalpies of combustion of cyclohexane $(C_6H_{12})$,cyclohexene $(C_6H_{10})$,and $H_2$ are $-3920, -3800$,and $-241 \, kJ \, mol^{-1}$ respectively. The heat of hydrogenation of cyclohexene is ...... $kJ \, mol^{-1}$.

The calorific value of hydrogen gas is $-143 \ kJ \ g^{-1}$. The standard enthalpy of formation of $H_2O$ will be $—$

The heat of combustion of $CH_{4(g)}$,$C_{(graphite)}$ and $H_{2(g)}$ are $-20 \ kcal$,$-40 \ kcal$ and $-10 \ kcal$ respectively. The heat of formation of methane is.......$kcal$.

Calculate the enthalpy of formation of sucrose $(C_{12}H_{22}O_{11})$ in $kJ \, mol^{-1}$ using the following data:
$(i) \, C_{12}H_{22}O_{11} + 12O_2 \to 12CO_2 + 11H_2O, \, \Delta H = -5200.7 \, kJ \, mol^{-1}$
$(ii) \, C + O_2 \to CO_2, \, \Delta H = -394.5 \, kJ \, mol^{-1}$
$(iii) \, H_2 + \frac{1}{2}O_2 \to H_2O, \, \Delta H = -285.8 \, kJ \, mol^{-1}$

Calculate the heat of formation of $PCl_{5(s)}$ from the following data:
$2P_{(s)} + 3Cl_{2(g)} \to 2PCl_{3(l)}; \Delta H_1 = -151.8 \ kcal$
$PCl_{3(l)} + Cl_{2(g)} \to PCl_{5(s)}; \Delta H_2 = -32.8 \ kcal$
Determine the enthalpy of formation for $PCl_{5(s)}$ in $kcal$.

The heat released when $0.8 \, g$ of carbon is converted to carbon dioxide is $x \, cal$. The heat released when $0.8 \, g$ of carbon is converted to carbon monoxide is $y \, cal$. If $x > y$,then the heat released when $1.86 \, g$ of carbon monoxide is converted to carbon dioxide will be: