There are three common states of matter: solid, liquid, and gas. A solid has a definite shape and volume, while a liquid takes the shape of its container but has a definite volume. A gas has no definite shape or volume. Physical forces like temperature and pressure can change the state of a substance between solid, liquid, and gas without altering its chemical properties. For example, adding heat causes water to change from a solid (ice) to a liquid (water) through melting, and from a liquid to a gas (water vapor) through boiling by further adding heat. Removing heat causes the reverse changes from liquid to solid through freezing.
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