I’m a bit confused on why higher elevations/decreased atmospheric pressure wouldn't affect the vapor pressure of a liquid-or have a negligible affect on vapor pressure.

With decreased atmospheric pressure, boiling point decreases, and a decrease in BP would increase vapor pressure. So isn’t atmospheric pressure changing the vapor pressure?

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    $\begingroup$ The only variable that affects the vapor pressure of given substance is its temperature. $\endgroup$ – Mathew Mahindaratne Dec 31 '18 at 22:14
  • $\begingroup$ Think about what vapour pressure is instead of using analogy $\endgroup$ – Alchimista Dec 31 '18 at 22:18

The boiling point of a liquid is the temperature such that the liquid's vapor pressure is equal to the atmospheric pressure. When you go to a higher altitude, the boiling point is lower not because the vapor pressure of the liquid at a given temperature has changed, but because there is less atmospheric pressure.

The vapor pressure of a liquid at a given temperature is an intrinsic property due to the equilibrium between the liquid and gas phase of that substance.


Vapor pressure does affect boiling point, but it doesn't go the other way. BP depends on VP, and VP depends on temperature. It is a one way relationship.


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