Phase Changes

There are 6 (or 7) phases changes that you should recognize and understand. They are:

Melting – when a solid turns into a liquid

Freezing – when a liquid turns into a solid (please notice that freeing does NOT mean cold -- molten steel turning into solid, glowing, red-hot steel is freezing. It is not cold)

Sublimation – when a solid turns directly into a gas. If you have seen dry ice (solid carbon dioxide) you have seen sublimation, but sublimation is more common than that. Ice cubes left in your freezer will shrink over time as the molecules of the ice go directly into the gas phase.

Deposition – when a gas turns into a solid. This is how frost and snow form, and why snow is so much prettier than sleet (frozen raindrops).

Condensation – when a gas turns into a liquid

Evaporation and Boiling – when a liquid turns into a gas. Both of these terms apply to the L--> G phase change, but they aren't exactly the same.

Evaporation is a surface property. Molecules on the surface of the liquid break free from the attractions of their neighbors and leave.

Boiling happens throughout the liquid. In this case, molecules have enough energy to break away from their neighbors and to push those neighbors aside and to form bubbles. This is much harder to do and the reason that even cold water will evaporate, but we (generally) have to warm things up to get them to boil.

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