Evaporation causes cooling.......

[Drew]

Does evaporation cause cooling because of molecules with high kinetic energy managing to leave the surface lowering the average temp of the fluid . Here their is no heat input.

OR

because of latent heat of vapourisation as the molecules absorb avalable heat to break the intermolecular bonds to evaporate, here their is heat input.

OR both?

[lana]

Evaporation means liquid turns into vapour.
This can be done in two ways. Assume a container with water in it. At the level of liquid two forces exists, one from inside the liquid and the other from the top of liquid interface. If these forces are equal then there is no change. If bottom force is higher (heat is applied to liquid) then you have evaporation at the liquid interface. If top force is lower (lower the pressure above the liquid, like vacuum) then the same thing happens.
In both cases heat is essential; in case one heat must be applied to the liquid and in case 2 required heat is absorbed from the liquid which makes it colder.

cheers

[Drew]

Is there a drop in temp in a dish of water that stands outside due to some molecules evaporating because they have a high enough kinetic energy and just leave the water leaving behind cooler molecules and the average temp of the molecules drops( causing the water temp to drop). Therefore no latent heat of evaporation occuring? Or do the 100 degree C molecules still require more heat to evaporate ( breaking the inter molecular bonds).

Therefore are their 2 reasons why water cools if left outside:

Firstly its loosing all the warmer molecules.
Secondly the warmer molecules require energy to evaporate which they take from the water its self?( latent heat of evaporation)

[Aik]

There is Maxwell's velocity distribution of molecules, that mean that molecules have different velosities (kinetic energies). Some molecules have enought energy to leave the water. When molecules leave the water they take away some energy from the water. Therefore, average energy of molecule is decrease... and temperature of water also decrease, because temperature depends on energy...

[Drew]

By that i take it that you agree?

Water temp drops for 2 reasons while evaporating:

Higher kinetic energy molecules can leave the water lowering the overall temp.
As they leave they further lower the temp by absorbing energy to evaporate?

[Aik]

There is one cause:


Higher kinetic energy molecules can leave the water lowering the overall temp.

And effect of thise cause is:

As they leave they further lower the temp by absorbing energy to evaporate