# How do you read the phase diagram of water?

Feb 17, 2017

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 $P = 1 \cdot a t m$, and we can see the phase transitions of water at $1 \cdot a t m$, 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 $\text{triple point}$, the conditions of temperature and pressure at which all 3 phases are in equilibrium, and the $\text{critical point}$, 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 $\text{critical points}$ are at highly non-standard conditions of temperature and pressure.