Phase diagrams tell how a given substance changes it’s phase with pressure and temperature. While most sources discuss this in detail, none of these mention whether or not evaporation is taken into account when drawing the diagrams . Any liquid can evaporate regardless of the temperature, given that the molecules have the needed kinetic energy. So, do phase diagrams take this into account?

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    $\begingroup$ Yes, pressure is taken into account. One way of measuring activities in molten mixtures is to measure the vapor pressure of the constituents over the melt. Since those activities determine the shape of the liquidus, clearly the vapor phase is considered/measured. $\endgroup$ – Jon Custer Nov 19 '17 at 16:15
  • $\begingroup$ A phase diagram depends on compositions, pressure and temperature. Since such a diagram is a 2D drawing of a 3D system, typically either the pressure or temperature will be constant. $\endgroup$ – MaxW Nov 19 '17 at 17:09

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