molar enthalpy of combustion of alkanes compare to alkanols (question)

[shademaker]

hey i did a practice exam and it asked which group of compounds (alkanes or alkanols) has a higher molar enthalpy of combustion and the answers stated alkanes did because they have weak inter molecular dispersion forces while alkanols have stronger hydrogen bonds. Wouldn't that mean alkanols have a higher molar enthalpy as more energy would be released from the breaking of their bonds? Also, the data book shows that alkanols have a higher molar enthalpy of combustion.

So are the answers for this exam wrong or am i just thinking of this the wrong way?
thanks

[unknown id]

The exam solutions are correct. The fact that the alkanols have stronger intermolecular bonds than alkanes means that they have a lower heat content (enthalpy) than the alkanes. Hence, more energy is released when alkanes are combusted than during the combustion of alkanols. This is also represented in the data book, where an alkane has a larger H value than its corresponding alkanol. For example, methane's molar enthalpy of combustion is -889 KJ/mol whereas that of methanol is only -725 KJ/mol.