Evaporation is simply molecules breaking into the air from a liquid. Molecules must achieve two things--'lifting' their weight, and interactions leaping with other molecules. In terms of size, smaller molecules should evaporate more quickly than bigger ones. With this in mind, ethanol molecules are larger than waters (see webpage above for observable oddities of water). Going on that ALONE, we would predict that of the two, ethanol should evaporate more slowly . However, this is not what is observed . Ethanol feels cooler on the skin and evaporates more quickly. We must look elsewhere for another factor! The secret lies in hydrogen interactions. water makes a ton of them; each of its atoms makes at least one. This creates a web of interactions holding each water molecule to several others-- and preventing evaporation. This is why water has an abnormally high boiling point for a small molecule. And it's related to the reason that unlike most solids, ice floats on its liquid (water). While we think of water as 'normal', it's actually a pretty outlandish liquid.