What would happen to the boiling point of water at 8,000 m above sea level, where air pressure is lower?

1 Answer
Nov 28, 2016

Well, of course, the boiling point would reduce.


The boiling point of a liquid (any liquid, indeed any material) is specified to be the temperature at which the vapour pressure of the liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The #"normal boiling point"# is specified when the ambient pressure is #"1 atmosphere"#. And thus it follows that when water is boiling at sea level (i.e. it is #100# #""^@C#), its #"vapour pressure"# is #1*atm#.

I would try very hard to take that definition on board, and test your understanding. It follows that if we reduce the ambient pressure, by say, going up a mountain, or in the lab by doing a vaccuum distillation, the temperature of the boiling point should reduce substantially. This underlies the principle of vacuum distillation (how?). It also explains why when you hike up a mountain, and cook your dinner, you normally have to boil it for a bit longer to cook it properly.

So the conclusion:

#"if ambient pressure is lower, the boiling point is"# #"necessarily lower."#