Heats of hydrogenation (to cyclohexane) : cyclohexene -120 kJ/mol, cyclohexa-1,4-diene -240 kJ/mol, cyclohexa-1,3-diene -232 kJ/mol, benzene -208 kJ/mol.
Calculate ΔH (kJ/mol, with sign) for cyclohexa-1,4-diene + $H_{2}$ $\to$ cyclohexene.

Question

Heats of hydrogenation (to cyclohexane) : cyclohexene -120 kJ/mol, cyclohexa-1,4-diene -240 kJ/mol, cyclohexa-1,3-diene -232 kJ/mol, benzene -208 kJ/mol.

Calculate ΔH (kJ/mol, with sign) for cyclohexa-1,4-diene + $H_{2}$ $\to$ cyclohexene.

TestHub · Accepted Answer

Cyclohexa-1,4-diene → cyclohexane is -240 kJ/mol and cyclohexene → cyclohexane is -120 kJ/mol. ΔH = -240 - (-120) = -120 kJ/mol.

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