MadSci Network: Chemistry

Re: why does atmospheric pressure is related to boiling point?

Date: Fri Apr 20 10:05:50 2001
Posted By: John Balbach, Physicist
Area of science: Chemistry
ID: 986305618.Ch

Actually, both the melting and boiling points are affected by atmospheric 
pressure, but the boiling point is more strongly affected.  You can get a 
feel for the reason by thinking of the problem in this way.  The boiling 
point of a material is a transition from a dense state to a state that is 
(roughly) 1000 times less dense.  Or, the material will need to occupy 1000 
times the volume.  Higher pressure resists the material from expanding in 
this way.  Lower pressure makes expansion easier.  The melting point is a 
transition from one dense state to another, and the densities are roughly 
equal, so pressure will have less of an effect.  The detailed explanation 
requires a lot of thermodynamics which you are not familiar with yet, but 
if you follow up with some physical chemistry or thermodynamics courses in 
college, you will learn all about this sort of thing.

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