Physical Changes

Did You Know?

When water boils it does not evaporate!

It’s true. We all may have been guilty of defining evaporation as the change of a liquid to a gas, but there is more to this definition.

Evaportation: The phase change of a liquid to a gas at a temperature below boiling point.

So what is going on when water boils? Juts that, it boils. Boiling describes the change of a liquid to a gas at the liquids boiling point. Another description of this change is vaporization.

Vaporization can be used to describe the change of a liquid to a gas at any temperature.

The subscripts after water tells you the state of matter, L for liquid, g for gas, and s for solid (ice).

For water to boil, liquid water must absorb heat. Notice that the change from liquid water to water vapor in the diagram requires heat. The process is labeled Vaporization.

The reverse of this reaction is called condensation and for this process to occur water vapor must loose heat.


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Challenge:  Do you know why things cook faster in a pressure cooker?