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.......$kcal$.

When $0.5 \ mol$ of $HNO_3$ reacts with $0.2 \ mol$ of $KOH$,the heat of neutralization is equal to ...... $kJ$.

Find the value of enthalpy of formation of $PCl_5(s)$ given the following thermochemical equations:
$1) \frac{1}{2} P_{4(s)} + 3Cl_{2(g)} \to 2PCl_3(\ell) ; \Delta H = -635 \ kJ$
$2) PCl_3(\ell) + Cl_{2(g)} \to PCl_{5(s)} ; \Delta H = -137 \ kJ$

For the reaction $2H_{2(g)} + O_{2(g)} \to 2H_2O_{(l)}$,the enthalpy change is $\Delta H = -571 \ kJ$. If the $H-H$ bond energy is $435 \ kJ \ mol^{-1}$ and the $O=O$ bond energy is $498 \ kJ \ mol^{-1}$,calculate the average bond energy of the $O-H$ bond in $kJ \ mol^{-1}$.

Calculate the heat of formation of $Ca(OH)_{2(s)}$ at $1.8\,^{\circ}C$ from the following data:
$CaO_{(s)} + H_2O_{(l)} \to Ca(OH)_{2(s)}$; $\Delta H_{1.8\,^{\circ}C} = -15.26\,K\,cal$
$H_{2(g)} + \frac{1}{2}O_{2(g)} \to H_2O_{(l)}$; $\Delta H_{1.8\,^{\circ}C} = -68.37\,K\,cal$
$Ca_{(s)} + \frac{1}{2}O_{2(g)} \to CaO_{(s)}$; $\Delta H_{1.8\,^{\circ}C} = -151.80\,K\,cal$

Which of the following is an exothermic reaction?