The heats of combustion of $CH_4, C_2H_6, C_2H_4$,and $C_2H_2$ at the same temperature are $-212.8, -373.0, -337.0$,and $-310.5 \, Kcal$ respectively. Which of these gases is the best fuel?

At $25^{\circ} C$ and $1 \, atm$ pressure,the enthalpy of combustion of benzene$_{(l)}$ and acetylene$_{(g)}$ are $-3268 \, kJ \, mol^{-1}$ and $-1300 \, kJ \, mol^{-1}$,respectively. The change in enthalpy for the reaction $3 C_2H_{2(g)} \rightarrow C_6H_{6(l)}$ is $..... \, kJ \, mol^{-1}$.

Calculate the difference between heat of combustion of carbon monoxide gas at constant pressure and at constant volume at $27^{\circ} C$ (in $cal$)? $(R = 2 \ cal \ K^{-1} \ mol^{-1})$

At the temperature $T$ $(K)$ for the reaction: $X_2O_{4(l)} \rightarrow 2XO_{2(g)}$,given $\Delta U = x \ kJ \ mol^{-1}$ and $\Delta S = y \ J \ K^{-1} \ mol^{-1}$. The Gibbs energy change for the reaction is: (Assume $X_2O_4$ and $XO_2$ are ideal gases)

Find the heat required to convert $10 \ g$ of ice at $0.0^{\circ} C$ into water at $30^{\circ} C$. (Enthalpy of fusion of ice $= 333.5 \ J \ g^{-1}$, $C_p$ of water $= 4.18 \ J \ g^{-1} \ K^{-1}$) (in $kJ$)

Standard enthalpy of vapourisation for $CCl_4$ is $30.5 \ kJ \ mol^{-1}$. Heat required for vapourisation of $284 \ g$ of $CCl_4$ at constant temperature is . . . . . . $kJ$. (Given molar mass in $g \ mol^{-1} ; C=12, Cl=35.5$ )