Sorry if I'm asking something stupid but I'm trying to understand where this energy gets from. As far as I could find, it is not a reaction as both chemicals left unchanged, so it might have something to do with hydrogen bonding but I can't connect these two facts together.
UPD: it is not homework question (I have a degree in a completely unrelated field) and I did try to find a reasonable explanation in search engines but with no luck. Atm my theory is that ethanol creates H-bonds with water and those bonds have less energy than the ones between H2O-H2O and the excess of the energy goes away as heat but I don't have anybody who could confirm or reject that. As for the forums - Stack Exchange branches to me is the most credible source so I went asking here first.