The heat of combustion of ethanol into carbon dioxides and water is $-327 \mathrm{kcal}$ at constant pressure. The heat evolved (in cal) at constant
volume and $27^{\circ} \mathrm{C}$ (if all gases behave ideally) is $\left(R=2 \mathrm{cal} \mathrm{mol}^{-1} \mathrm{~K}^{-1}\right)$
$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}_{(\ell)}+3 \mathrm{O}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{CO}_{2(\mathrm{~g})}+3 \mathrm{H}_{2} \mathrm{O}_{(\ell)}$
$\Delta \mathrm{n}_{g}=2-3=-1$
$\Delta_{\mathrm{c}} \mathrm{H}=\Delta_{\mathrm{c}} \mathrm{U}+\left(\Delta \mathrm{n}_{\mathrm{g}}\right) \mathrm{RT}$
$\Delta_{c} H=\Delta_{c} U-R T$
$\Delta_{\mathrm{c}} \mathrm{U}=\Delta_{\mathrm{c}} \mathrm{H}+\mathrm{RT}$
$=-327 \times 10^{3}+2 \times 300$
$=-326400 \mathrm{cal}$
$\therefore$ Heat evolved
$=326400 \mathrm{cal}$
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