The enthalpy of combustion at of , cyclohexane(l) and cyclohexene(l) are –241, –3920 and –3800 kJ/mo — Thermodynamics and Thermochemistry Chemistry Question
Question
The enthalpy of combustion at $25^\circ\text{C}$ of $\text{H}_2\text{(g)}$, cyclohexane(l) and cyclohexene(l) are –241, –3920 and –3800 kJ/mol, respectively. The enthalpy of hydrogenation of cyclohexene(l) is
Answer: A
💡 Solution & Explanation
Hydrogenation reaction: $\text{C}_6\text{H}_{10} + \text{H}_2 \to \text{C}_6\text{H}_{12}$. Using Hess's law with combustion data: $\Delta H_{rxn} = \Delta H_c(\text{C}_6\text{H}_{10}) + \Delta H_c(\text{H}_2) - \Delta H_c(\text{C}_6\text{H}_{12}) = -3800 + (-241) - (-3920) = -4041 + 3920 = -121\text{ kJ/mol}$.
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