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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