The standard enthalpy of combustion for solid elemental carbon oxidizing to is . Determine the total — Thermodynamics and Thermochemistry Chemistry Question
Question
The standard enthalpy of combustion for solid elemental carbon oxidizing to $CO_2(g)$ is $-393.5 \text{ kJ/mol}$. Determine the total magnitude of heat released (in kJ, to one decimal place) to the surroundings upon the complete, stoichiometric formation of $35.2 \text{ g}$ of $CO_2(g)$ from carbon and excess oxygen.
💡 Solution & Explanation
The thermochemical equation is: $C_{(s)} + O_2(g) \rightarrow CO_2(g)$, with $\Delta_c H^\circ = -393.5 \text{ kJ/mol}$. First, calculate the moles of carbon dioxide produced using its molar mass ($44 \text{ g/mol}$): $n = \frac{35.2 \text{ g}}{44 \text{ g/mol}} = 0.8 \text{ mol}$ of $CO_2$. Because $1 \text{ mol}$ yields $393.5 \text{ kJ}$ of heat, the total heat released by $0.8 \text{ mol}$ is $0.8 \text{ mol} \times 393.5 \text{ kJ/mol} = 314.8 \text{ kJ}$.