i'am having some difficulties with the concept of cooling evaporation here's some of the ideas that i found and i want to figure out how accurate they are:

1-the cooling evaporation happens when a liquid evaporate into the surrounding air causing the air to cool off

2-evaporation happens because of the randomly movement of molecules cause
some of these molecules have higher kinetic energy so they can escape thus when evaporating the LIQUID cools off cause its total kinetic energy has decreased

3-evaporation happens because of the heat absorbed from the surrounding air thus when it happens the AIR cools off

  • $\begingroup$ All three of those things happen simultaneously. $\endgroup$ Oct 20, 2016 at 19:00

1 Answer 1


Evaporative cooling happens because of the latent heat of evaporation. What happens qualitatively is that as energy is added to a fluid, the molecules vibrate more vigorously: we experience this as heat. However, when the fluid transitions from liquid to gas, the temperature stays the same even though we are adding more energy. This is because the energy is absorbed into breaking up the molecular bonds of the fluid.

In general, there are a range of different energy levels available in a fluid, with some molecules having higher energy than others at a microscopic level. These molecules contribute to the temperature which is basically the average of the molecular energy. When the molecules evaporate, they need to absorb the latent heat from their surroundings, normally because they are the molecules that happen to have higher energies. That leaves the surrounding molecules with a lower average energy.

  • $\begingroup$ actually am a little confused $\endgroup$ Oct 20, 2016 at 20:25
  • $\begingroup$ did the molecule had higher energy in the first place,or did it absorbed this energy from the surrounding in order to escape the surface? *note that am not talking about boiling ,just evaporation at room temperature $\endgroup$ Oct 20, 2016 at 20:28
  • $\begingroup$ It can happen either way. The net effect is the same. Some thermal energy is lost to latent heat of evaporation. Normally, the evaporation is the higher energy molecules. In practice, these molecules are in equilibrium (so some evaporating and some condensing at the same rate). But if you, for example, blow air on the surface, the molecules keep evaporating because the gaseous molecules just above the surface get removed. The removal of these gaseous molecules takes heat away because they are not able to re-condense into the liquid (when they would give back their heat). $\endgroup$
    – Dr Xorile
    Oct 20, 2016 at 20:36
  • $\begingroup$ thanks for replaying,does both liquid and surrounding get cooled down by this process ? $\endgroup$ Oct 21, 2016 at 12:13

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