The heat of combustion of carbon to CO₂ —393.5 kJ/mol. The heat released upon formation of 35.2 g of CO₂ from carbon and oxygen gas is 

$$\begin{gathered} \mathrm{C}+{\mathrm{O}}_2\to {\mathrm{CO}}_2+393.5\mathrm{kJ}/\mathrm{mol} \\ 12 \mathrm{g} 44\mathrm{g} \\ 44\mathrm{g} \mathrm{is} \mathrm{formed} \mathrm{from} 12\mathrm{g} \mathrm{of} \mathrm{carbon} \\ 35.2\mathrm{g}\text{ is formed from }\frac{12\times 35.2}{44}\mathrm{g}\text{ of }\mathrm{C} \\ =9.6\mathrm{g}\text{ of }\mathrm{C}=9.6/12=0.8\mathrm{mole} \\ 1\text{ mole release heat }393.5\mathrm{kJ} \\ 0.8\text{ mole release heat }=393.5\times 0.8 \\ =314.8\mathrm{kJ}\approx 315\mathrm{kJ} \end{gathered}$$