Does atmospheric pressure affect the saturated vapor pressure ?

  1. Jano L.

    Jano L. 1,240
    Gold Member

    When the Clausius-Clapeyron equation for saturation vapor pressure over liquid water is derived via the Carnot cycle, it is usually assumed that there is only gaseous water above the liquid. The other atmospheric gases are neglected.

    However, in common settings (lake, glass of water...), the atmospheric gases exert much higher pressure on the liquid surface than the water vapor. Does this large pressure affect the saturation vapor pressure somehow? I guess that the correction is small, perhaps since the additional atmospheric pressure is too low to change the volume of liquid water significantly...
  2. jcsd
  3. mfb

    Staff: Mentor

    For ideal gases, I think there should be no change.
    Gases are not ideal, of course - they need some volume (reducing the volume available for water a bit), they have some interaction (I guess this gives a bit more water, but I don't know). In real air, you also have dust particles and so on.
  4. Jano L.

    Jano L. 1,240
    Gold Member

    Yes, that is similar to what I was thinking.

    On the other hand, when applied to solid-liquid equilibrium, the "p" in the C-C equation refers to total liquid pressure. It is a bit strange that for liquid-gas equilibrium, the "p" in the C-C equation refers to partial pressure of the vapor, not to the total liquid pressure.
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