Question
Mon January 16, 2012 By: Nevil Shah

I am not understanding how can vapour coexist at temperature 273.16 K?

Expert Reply
Tue January 17, 2012
At Zero degrees celsius or 273.16 K temperature water is in the process of changing from a solid state into the liquid phase or vice versa. Molecules in the liquid phase can loose a bit of energy and solidify while solid water (ice) can gain some energy and melt. This can be seen in melting ice where the solid ice exists for some time while the exposed surface melts.
Molecules in a liquid don't all have the same energy. The energies of the molecules can vary from a finite minimum to a very large value. The average energy of the molecules gives us the temperature of the liquid. At a certain energy molecules will have enough energy to evaporate, even if the water temperature is 0 degrees celsius. Because of these two effects it is possible for the water to exist as solid, liquid and gas at the same time.

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