Enthalpies of combustion of , and are –210, –370 and –526 kcal/mol, respectively. Enthalpy of combus — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Adding a $-\text{CH}_2-$ group increases the magnitude of combustion enthalpy. $\Delta(\text{C}_2\text{H}_6 - \text{CH}_4) = -160\text{ kcal}$. $\Delta(\text{C}_3\text{H}_8 - \text{C}_2\text{H}_6) = -156\text{ kcal}$. Using an average increment of approximately $-158\text{ kcal}$ per $-\text{CH}_2-$ group: Hexane ($\text{C}_6\text{H}_{14}$) has 3 more $-\text{CH}_2-$ units than propane. Predicted $\Delta H_c \approx -526 + 3(-158) = -526 - 474 = -1000\text{ kcal/mol}$.