The standard enthalpies of combustion of , , and are -1409.5, -1558.3, and -285.6 kJ/mol respectivel — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

The hydrogenation reaction is $C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)$. By Hess's Law using combustion data: $\Delta H_{rxn} = \sum \Delta H_c(reactants) - \sum \Delta H_c(products) = [-1409.5 + (-285.6)] - [-1558.3] = -1695.1 + 1558.3 = -136.8$ kJ/mol.