Energy changes
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Why does propan-2-ol have a lower enthalpy change of combustion than propan-1-ol? I have looked everywhere and found nothing. They both have the same number of each type of bond, is it something to do with hydrogen bonds?
Ulex says ...
The difference is only about 15 kJ mol–1 on values of about 2000 – well within experimental error, I would think.
The difference could be due in part to differences in the enthalpy change of vaporisation caused, as you surmise, by different intermolecular forces between molecules that are not the same shape.
Another possibility is variation in bond strength for similar bonds in different molecular environments. The bond energies in data tables are only averages. In fact they vary slightly from compound to compound.
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updated: 10 December 2003
