Question

The heat of formation of benzene is __________ kJmol$^{-1}$. (Nearest integer)

Answer 1

48

Answer 2

The balanced combustion equation for benzene is C$_6$H$_6$(l) + $\frac{15}{2}$O$_2$(g) $\rightarrow$ 6CO$_2$(g) + 3H$_2$O(l). Using the thermochemical relation $\Delta H_{combustion} = \sum \Delta H_f(\text{products}) - \sum \Delta H_f(\text{reactants})$: $-3267.0 \text{ kJ/mol} = [6 \times (-393.5) + 3 \times (-286.0)] - [\Delta H_f(\text{C}_6\text{H}_6) + \frac{15}{2} \times 0]$ $-3267.0 = [-2361.0 - 858.0] - \Delta H_f(\text{C}_6\text{H}_6)$ $-3267.0 = -3219.0 - \Delta H_f(\text{C}_6\text{H}_6)$ $\Delta H_f(\text{C}_6\text{H}_6) = -3219.0 + 3267.0 = 48.0 \text{ kJ/mol}$.