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

💡 Solution & Explanation

In a homologous series, the enthalpy of combustion increases almost linearly with the number of CH2 groups. The difference between $CH_4$ and $C_2H_6$ is: -370 - (-210) = -160 kcal/mol. The difference between $C_2H_6$ and $C_3H_8$ is: -526 - (-370) = -156 kcal/mol. The average increase per -CH2- group is approx. -158 kcal/mol. Hexane (C6H14) has 3 more CH2 groups than propane ($C_3H_8$). Thus, predicted enthalpy of combustion of hexane: δ H_comb = -526 + 3 * (-158) = -1000 kcal/mol.