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Q & A: sublime

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Most recent answer: 10/22/2007
Q:
How does gas turn into a solid?
- Britt (age 11)
A:
Sometimes a solid turns to a gas by 'subliming'. The molecules or atoms of the solid simply fly off the surface (thanks to thermal energy- the jiggling that things with a temperature have) into a gas. At ordinary pressures, the CO2 in dry ice does that. Other times, the solid first melts to a liquid, in which the molecules still stick together but not in a regular pattern. Then molecules evaporate away from the liquid. Water under ordinary pressure does that. However, if there are few of the molecules around in the gas, some subliming will occur even for solids that will melt to liquids. For example, in most freezers ice cubes will gradually sublime away even though they're too cold to melt.

Whoops- I realize now you asked how a gas turns into a solid, not how a solid turns into a gas. Take everything I wrote and run it in reverse.

Mike W.

(published on 10/22/2007)

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