Understanding Boiling Point: Factors That Affect Liquid Vapor Pressure

[swiss729]

Hello!

I often read that the boiling point of a liquid is when its vapor pressure is equal to the atmospheric pressure. What I don't understand is why they never take the pressure of the water into consideration? Doesn't water pressure increase as depth increases and wouldn't this have to be overcome in addition to the atmospheric pressure? Thanks for the help!

:)

 

[chemisttree]

Yes. The temperature of the water at the bottom of the flask will have a slightly different boiling point than the water at the surface. Usually the flask is being heated from the bottom so that part is hotter than the water near the top. The shape of the flask can seriously change the BP by the way. That is how geysers work. Water at the bottom of the crevice (think of it as a column of water) is superheated and expands, pushing out the water from the top of the column. Once that water's weight has been removed to a certain extent, explosive boiling results shooting the remaining water into the sky.

In the lab, the effect is very small and is neglected.