Heat of reaction at constant pressure is represented by ΔH

Heat of reaction at constant volume is represented by ΔU

${\mathrm{C}}_{10}{\mathrm{H}}_8\left(\mathrm{s}\right)+12{\mathrm{O}}_2\left(\mathrm{g}\right)⟶10{\mathrm{CO}}_2\left(\mathrm{g}\right)+4{\mathrm{H}}_2\mathrm{O}$

We known that $\mathrm{\Delta H}=\mathrm{\Delta E}+{\mathrm{\Delta n}}_{\mathrm{g}}\mathrm{RT}$

${\mathrm{\Delta n}}_g=10-12=-2$

$\mathrm{\Delta H}=-1228.2\times {10}^3+\left(-2\right)\times 2\times 298$

$=-1229393 \mathrm{Cal}$

$=-1229.39 \mathrm{kcal}$