The combustion of carbon to form carbon dioxide is given by the reaction: $\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)}; \Delta H = -393.5 \text{ kJ/mol}$ This means that the formation of $1 \text{ mole}$ of $\text{CO}_2$ ($44 \text{ g}$) releases $393.5 \text{ kJ}$ of heat (or the enthalpy change is $-393.5 \text{ kJ}$). Number of moles in $35.2 \text{ g}$ of $\text{CO}_2$ = $\frac{\text{Given mass}}{\text{Molar mass}} = \frac{35.2 \text{ g}}{44 \text{ g/mol}} = 0.8 \text{ mol}$. The heat released (enthalpy change) for the formation of $0.8 \text{ mol}$ of $\text{CO}_2$ is: $\Delta H = 0.8 \text{ mol} \times (-393.5 \text{ kJ/mol}) = -314.8 \text{ kJ} \approx -315 \text{ kJ}$.