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.

 

[quicknote]

Hello there! You bring up a great point about the role of water pressure in boiling point. While it is true that the boiling point of a liquid is when its vapor pressure is equal to the atmospheric pressure, it is important to note that this is only true for water at sea level. As you mentioned, the pressure of water increases as depth increases, which means that the boiling point of water would also change at different depths. However, for most practical purposes, the difference in water pressure at different depths is negligible and does not significantly affect the boiling point of water. This is because the atmospheric pressure at sea level is much greater than the pressure exerted by the water itself. Therefore, the atmospheric pressure is the dominant factor in determining the boiling point of water. I hope this helps clarify any confusion about the role of water pressure in boiling point. Keep asking great questions!