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From my lecture course it was indicated that this is what a phase diagram looks like. enter image description here

Is this diagram applicable to water? All the ones I can find online seem to use pressure on the y axis as oppose to G. If if it is applicable to water, where is the triple point on the graph? I understand it's where the 3 phase lines intersect but this doesn't appear to occur on this type of graph.

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  • $\begingroup$ I'm going to get out my steam tables and calculate the Gibbs free energy as a function of temperature along the liquid-vapor saturation line. ( The steam tables give values for the specific entropy and specific enthalpy for each state. From that, you can calculate G. ). I suggest you do the same. Sounds interesting. The steam tables for superheated states can also be used to determine which side of the saturation line the vapor and the liquid reside. $\endgroup$ – Chet Miller Feb 26 '18 at 22:35
  • $\begingroup$ I made the calculation, and, unlike the figure in the post, the saturation line is a smooth curve. But the other features are the same. The superheated vapor lies below the saturation line, and the compressed liquid and solid are above the line $\endgroup$ – Chet Miller Feb 26 '18 at 23:09
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Phase diagrams are not limited to temperature vs pressure. They can be made with any set of thermodynamic quantities. The diagram in your question is for a particular pressure at which the liquid phase exists. If you changed the pressure, the lines would shift. A triple point will be represented by all three lines intersecting through the same point.

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