Energy changes and bonding
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My question is regarding the study task about bonding in benzene and cyclohexene in topic 12 found on page 276 of the Nuffield Student Book. I understand that I need to use Hess's law to solve the problem but I don't know where to start.
Jenkin replies
You don’t need to use Hess’s Law.
The stem (first sentence and equation) of the question tells you the enthalpy change when one mole of cyclohexene is converted into benzene by reaction with hydrogen, that is when one mole of C=C bonds are changed into C–C bonds by the addition of hydrogen.
So, in part 1 of the task, you use this data to predict the enthalpy change when three moles of C=C bonds are hydrogenated (no catch, it’s very easy!).
Then, in part 2, you need to compare the value of DH you have just calculated with -208 kJ mol-1, and use the comparison to answer part 3.
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updated: 25 January 2006
