Understanding Boiling Point: Factors That Affect Liquid Vapor Pressure

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The boiling point of a liquid is defined as the temperature at which its vapor pressure equals atmospheric pressure. However, the discussion highlights that water pressure increases with depth, which can influence the boiling point. In a heated flask, the water at the bottom is typically hotter than at the surface, leading to variations in boiling point. The shape of the flask can also affect boiling point due to the pressure dynamics involved. This principle is illustrated by geysers, where superheated water at the bottom expands and forces water out from the top, leading to explosive boiling. In laboratory settings, the impact of water pressure on boiling point is generally minimal and often overlooked.
swiss729
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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!

:)
 
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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.
 

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