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Asked by to Alan, Deepak, Francesca, Lilly, Nick on 17 Mar 2014. This question was also asked by .
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Deepak Kar answered on 17 Mar 2014:
It is called sublimation. Basically it happens if the pressure and temperature is such that the molecules get enough energy to bypass the liquid state for that material. For Iodine, in usual room temperature and pressure, that is the case.
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Alan Fitzsimmons answered on 17 Mar 2014:
This is called sublimation, and it depends on the substance you’re using, the temperature, and the pressure.
For example, you know water normally boils into a gas at 100 degrees celsius? Well, if you go up a mountain it boils at a lower temperature because the air pressure is lower. (When I’m using the telescope on Mauna Kea in Hawaii it only boil at 77 degrees celsius, so my tea always tastes different up there!).
As you go higher and the air pressure gets lower, the water boils at lower and lower temperatures. If you go into space, there the water will turn into gas immediately. So liquid water cannot exist in a vacuum, and if you expose ice to sunlight, it immediately starts turning into a gas. So water sublimates in space.
Guess what? That’s how icy comets lose the material from their surfaces and make their tails.
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Francesca Day answered on 17 Mar 2014:
Good question! Most substances will do this at the right temperature and pressure. It happens because the molecules have enough energy to overcome the attractive forces between them entirely and become a gas. With iodine, this is the case at room temperature and pressure.
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Nick Wright answered on 21 Mar 2014:
Its a process called sublimation and if the conditions are right its just a case of the solid being able to make both transitions (melting first, then evaporating) straight away.
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