In a constant volume calorimeter, 3.5 g of a gas with molecular weight 28 was burnt in excess oxygen at 298.0 K. The temperature of the calorimeter was found to increase from 298.0 K to 298.45 K due to the combustion process. Given that the heat capacity of the calorimeter is 2.5 kJ ${\mathrm{K}}^{-1}$ , the numerical value for the enthalpy of combustion of the gas in kJ $\mathrm{m}\mathrm{o}{\mathrm{l}}^{-1}$ is