| MadSci Network: Chemistry |
What makes something
sublimate?
The correct verb is
sublime, not sublimate.
I am doing an idependant project for science, and I am finding many
experiments to do with sublimation, but not an explanation itself of
what makes something sublimate. Can someone please help me? I know
it's basically a solid turning into a gas without becomeing a liquid,
but WHY do things sublimate? Also, what is the opposite of
sublimation?
A substance sublimes when the external pressure is too low for the liquid state to exist at any temperature. This pressure differs for different substances; for example, liquid water can exist at "room temperature" (25°C) at pressures down to about 5% of normal sea-level pressure. But carbon dioxide cannot exist as a liquid at any temperature unless the pressure is greater than about 4.1 atmospheres; carbon dioxide is commonly stored, as a liquid, at a pressure of about 15 atmospheres.
Low pressure can be thought of as the normal state of nature. Most of the universe (if you consider space rather than matter) has a pressure so low that liquids cannot exist.
You may want to read my recent answer on the phase diagram of water. The vapor pressure of any condensed material tells you the minimum external pressure at which the solid/liquid can coexist with its vapor.
| Dan Berger | |
| Bluffton College | |
| http://cs.bluffton.edu/~berger |
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