Question

How do you read the phase diagram of water?

Answer 1

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

Explanation:

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.