|MadSci Network: Chemistry|
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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