/sci/ - Science & Math

Ok, so this one has been bugging me since Introduction to Chemistry years ago.

>Isolated room at 1 atm / 25 degrees Celsius and 0 % relative humidity
>Droplets of water at floor also at precisely 25 degrees Celsius
>No temperature difference between surroundings and the droplets
>Thus no heat transfer
>Yet the droplets vaporize

Where does this energy to change phase come from?

Suppose you have a few droplets of water on a surface in a room with dry air. The water, surface and air are at thermal equilibrium at comfortable 298 K and 1 bar.

By experience we know that the water will eventually evaporate into the air due to vapour pressure. This is, of course, a change in phase, and should require 2257 kJ/kg of energy to happen.

Most often this energy in in the form on heat, and since the water is still, it can't be due to viscous forces either. Heat, of course, is thermal energy moving from a point with higher temperature to a point with lower temperature. No temperature difference, no heat transfer.

The water will evaporate since the surrounding air is dry. The question is: where does the latent heat of vaporization come from?