Question

The heat of combustion of solid benzoic acid at constant volume is $-321.30kJ$ at ${27}^{o}C$. The heat of combustion at constant pressure is:

• A. $-321.30-300R$
• B. $-321.30+300R$
• C. $-321.30-150R$
• D. $-321.30+900R$

Answer 1

The correct option is C $-321.30-150R$

$C_6{H}_{5}COOH\left(s\right)+\frac{15}{2}{O}_2\left(g\right)⟶7C{O}_2\left(g\right)+3H_{2}O\left(l\right)$

$\Delta n=\Delta n_p-\Delta n_r$

$\Delta n=7-\frac{15}{2}=-\frac{1}{2}$

$\Delta H=\Delta U+\Delta nRT$

$=-321.30-\frac{1}{2}\times R\times 300$

$=-321.30-150R$