Why does evaporating water cause some water to be cooled and form ice?

[i_love_science]

Homework Statement

Some water is placed in a sealed container connected to a vacuum pump and the pump is turned on. The water appears to boil and then freezes. Explain these changes by using the phase diagram for water.

Relevant Equations

phase diagram of water

Answer:

I know that when water evaporates, it absorbs heat, that's why the process is endothermic. I don't understand why the water would be cooled and some ice would form, when the water is supposed to evaporate. What causes some water to be separately cooled instead of evaporated?
Thanks.

 

[Borek]

Where does the heat to evaporate water come from?

 

[i_love_science]

Where does the heat to evaporate water come from?

Other water molecules? Is this a transfer of heat from certain water molecules to others, causing some water to freeze while others to evaporate?
And is there some selectivity in this process? Thanks.

 

[Borek]

Other water molecules? Is this a transfer of heat from certain water molecules to others, causing some water to freeze while others to evaporate?

Yes, that's exactly what is happening.

And is there some selectivity in this process?

I am not sure what you mean by that.

Evaporating water will "steal" heat from its surroundings, no matter what they are, cooling everything around.

To be precise: questions makes and untold assumption that the process is adiabatic (or quick enough to be adiabatic in a good approximation) and no heat is exchanged with the surroundings. It is a reasonably good assumption though.