Alcohol vs Water Evaporative Cooling

Name: Marc
Status: educator
Grade: K-12
Location: AK

Question: When rubbing alcohol evaporates, it 'feels' colder than
water. Is this because it requires more energy for a phase change
than water?
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Marc,

You are correct in thinking that the difference in "feel" is a function 
of the heat of vaporization. Iso-propyl alcohol (the main component of 
rubbing alcohol) has a dH = 44 kJ/mol versus the dH of water which is 
41 kJ/mol. Vaporizing alcohol requires more energy. However, another factor 
is the specific heat of iso-propyl alcohol is 154 J/mol.K, that of water is 
76 J/mol.K. This means for every degree temperature change in alcohol, a lot 
more energy is absorbed.

Greg (Roberto Gregorius)
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