Question

$C_6{H}_6\left(g\right)+\frac{15}{2}{O}_2\to 6C{O}_2\left(g\right)+3H_{2}O\left(l\right)$
The heat liberated on complete combustion of $7.8$ benzene is $327$ KJ. This heat has been measured at constant volume and at ${27}^0$C. Calculate heat of combustion of benzene at constant pressure at ${27}^0$C.

Answer 1

$C_6{H}_6+\frac{15}{2}{O}_2\to 6C{O}_2+3H_{2}O$

$\left(g\right)$ $\left(g\right)$

$\Rightarrow △n_{\left(g\right)}=6-\frac{15}{2}=\frac{-3}{2}$

$\Rightarrow △H=△E+△n_{\left(g\right)}RT$

$7.8g$ of Benzene liberates $327kJ$ of heat.

$78g\left(1mol\right)$ of Benzene liberates $3770kJ$ of heat.

$\therefore △H=-3270+\left(\frac{-3}{2}\right)\left(8.314\right)\left(300\right)\left(10.3\right)$

$=-3273.74kJ$

Hence, the answer is $-3273.74kJ.$