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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
    Commented Dec 31, 2018 at 22:14
  • $\begingroup$ Think about what vapour pressure is instead of using analogy $\endgroup$
    – Alchimista
    Commented Dec 31, 2018 at 22:18

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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.

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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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