I'm confused as to what exactly is vapor pressure and saturation pressure. From what I understand, vapor pressure is just the equilibrium pressure of a vapor above a liquid at some temperature. Is this not also the definition of the saturation pressure (ie. an equilibrium pressure at some temperature)? Does a system always tend towards its saturation pressure? Or is it that there is one saturation pressure at some specific temperature, and that upon increasing the temperature, the vapor pressure will eventually reach the saturation pressure? Is the saturation pressure dependent on overall pressure?

  • $\begingroup$ According to Wikipedia they are the same $\endgroup$
    – Annibale
    Oct 7, 2017 at 6:56

1 Answer 1


You can have vapour when there is no liquid present and that vapour would exert a vapour pressure.

If however you have liquid and vapour present in dynamic equilibrium with one another then the pressure exerted by the vapour is the saturated vapour pressure.

So start off with a container with only vapour in it.
The vapour exerts a vapour pressure.

Now do something eg add liquid, cool the vapour, reduce the volume of the container, etc, so that there is also liquid in the container.
Then the pressure exerted by the vapour is the saturated vapour pressure.


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