Cyclohexene + H–H Cyclohexane. The bond energies (in kJ/mol) at are , , , . From these data, the val — Thermodynamics and Thermochemistry Chemistry Question
Question
Cyclohexene + H–H $\to$ Cyclohexane. The bond energies (in kJ/mol) at $25^\circ\text{C}$ are $\text{C}-\text{C} = 346$, $\text{C}-\text{H} = 413$, $\text{H}-\text{H} = 437$, $\text{C}=\text{C}; 611$. From these data, the value of $\Delta H$ at $25^\circ\text{C}$ for the above reaction is
Answer: B
💡 Solution & Explanation
Bonds broken: 1 $\text{C}=\text{C}$ (611) and 1 $\text{H}-\text{H}$ (437). Bonds formed: 1 $\text{C}-\text{C}$ (346) and 2 $\text{C}-\text{H}$ ($2 \times 413$). $\Delta H = \Sigma \text{BE}_{\text{broken}} - \Sigma \text{BE}_{\text{formed}} = (611 + 437) - (346 + 826) = 1048 - 1172 = -124\text{ kJ/mol}$.
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