The heat of combustion of benzene at 27°C found by bomb calorimeter i.e. for the reaction${\mathrm{C}}_6{\mathrm{H}}_{6\left(\mathrm{l}\right)}+7\frac{1}{2}{\mathrm{O}}_{2\left(\mathrm{g}\right)}\to 6{\mathrm{CO}}_{2\left(\mathrm{g}\right)}+3{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}$is 780 K.Cal mol^–1. The heat evolved on burning 39g of benzene in an open vessel wil be