What will happen to water at $0^\circ$ Celsius kept in large evacuated chamber Suppose some water is kept at $0^\circ$, in a glass (ideal container, if necessary). Now it is placed in a large evacuated chamber. What will happen?
I think some water will vaporize, some will freeze and rest will remain liquid. But then I think how can water exist in liquid phase in such a high volume. Then I think I am confused, so I must ask it here.
 A: When one says the boiling point is x degrees at such a pressure, what it means is that it holds a partial vapour pressure up to this.  Heat is fed in to make water into steam, even at room temperature, but it's so slight you don't notice it in the speciic heat.
When you have a large volume, a large amount of water is turned into steam, until the correct vapour pressure is met.  For tiny volumes, the pressure can get high quickly, and water can be heated beyond 100 centigrade, right up to 373 c.  
For a small amount of water at 32 Fahr, it will all vapourise if the pressure is less than the boiling pressure at 0c.  
A: It depends on the walls.  If they are truly insulated, no heat will flow in or out.  The water that freezes raises the temperature, while the water that evaporates lowers the temperature.  The triple point of water is $0.01^\circ C, 611.73$ Pascals.  If the chamber is very large, relatively much of the water will evaporate and the temperature will be below the triple point.  You will form an ice/vapor equilibrium.  If the chamber is not much larger than the water volume, a little water will evaporate, more water will freeze, and you will be at the triple point. Since the volume of water and ice are not very different, you can calculate how much vapor is there from the total mass of water.  Then you can calculate the amount of ice to make the temperature right.  You won't be far wrong.  If you want, you can iterate looking at the change in the volume of water/ice.
