phases of matter

1. The states in which matter can exist: as a solid , liquid , or gas . When temperature changes, matter can undergo a phase change, shifting from one form to another. Examples of phase changes are melting (changing from a solid to a liquid), freezing (changing from a liquid to a solid), evaporation (changing from a liquid to a gas), and condensation (changing from a gas to a liquid). ( See boiling point , condensation point , freezing point , melting point , triple point , and vaporization .)