Subject: Why the molar mass of an alcohol effects its enthalpy of combustion

Hello. I had to do a group assignment at school relating to the topic 
of 'super market'; wherein within each group was a chemist, biologist and 
physicist.  We chose the topic of alcohol, and for this I tested the burning 
efficiency of various alcohols, making the independent variable the molar mass 
of the alcohol.  I did the experiment, and concluded that as the molar mass 
increases, so too does the enthalpy of combustion, and hence efficiency as a 
fuel.  I was just wondering why the molar mass affected the enthalpy.  Thankyou

Re: Why the molar mass of an alcohol effects its enthalpy of combustion