How do you read the phase diagram of water?

1 Answer
anor277
Feb 17, 2017

Well, first you need a phase diagram........and then you must decide on conditions of temperature and pressure.

Explanation:

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Typically, pressure is plotted against temperature, and here we examine the phase of the water under different conditions of temperature and pressure. Of course, we can draw the ordinate #P=1*atm#, and we can see the phase transitions of water at #1*atm#, i.e. at #0# #""^@C# and #100# #""^@C#.

The fact that the slope of the ice-water transition is NEGATIVE is a very unusual property, and it can show that ice is less DENSE than water (I think the slope of the graph is highly exaggerated!).

Depicted on the graph are the #"triple point"#, the conditions of temperature and pressure at which all 3 phases are in equilibrium, and the #"critical point"#, the conditions of temperature and pressure at which the densities of the liquid phase, and gaseous phase become equal, and you can no longer distinguish between the 2 phases. Clearly, these #"critical points"# are at highly non-standard conditions of temperature and pressure.

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