3

I have learnt that, most objects still have energy in their atoms until the temperature reaches absolute zero. In other words, everything has energy around us. Now, that in mind if I go to antartica, the land is solid ice however below due to pressure it remains water which is cold yet it still moves.

That in mind, that should tell me particles must be hitting each other and such that in mind, water should evaporate yet it does not. I asked a similar question: Why does evaporation take place?

Yet this is an phenomena which I never truly understand as it too should follow the basic rules of physics as well so it too should evaporate as a result of Maxwell-Boltzmann distribution.

Community
  • 1

3 Answers3

4

The equilibrium vapor pressure of water vapor over ice is well known and easy to google for (http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm is one possible link). It is slightly lower than the equilibrium vapor pressure of water vapor over liquid. Ice does not evaporate - it sublimates under those conditions. The equilibrium vapor pressures are the result of the balance of entropy gain in the vapor phase vs the enthalpy required to change the phase of a water molecule. This is the thermodynamics of the problem. The kinetics (how long would it take to achieve equilibrium) is a result of the M-B distribution.

Jon Custer
  • 7,986
2

Solid ice does sublimate (go directly from a solid to a gas) over time, but the process is fairly slow. You can see this simply by leaving ice in your freezer for several days. The ice will gradually sublimate away. Wind and dry air both speed up this process, but it is still nowhere near as fast as evaporation under most circumstances. In Antarctica, some ice does sublimate, but not much, and overall, the system is in equilibrium so the average ice level doesn't change much. (This is of course ignoring global warming, which is causing the polar ice caps to deteriorate.)

JotThisDown
  • 1,474
2

Look at the phase diagram of water:

enter image description here

You can see there is a region where ice and water vapor can coexist. Ice turning to vapor without melting is called sublimation. The energy needed for a water molecule to break the bonds holding the ice together is quite large - so the probability that a thermal fluctuation is big enough for a molecule to escape is small (but non-zero), and is a function of temperature (the colder, the less likely).

If there is moisture in the air, the reverse process ( water turning into ice) is thermodynamic ally much more favored - the other direction only happens if the air is extremely dry. Another way of putting this: the partial pressure of water vapor in air below zero Celsius is very small.

Floris
  • 119,981