Taken from About.com - Chemistry
Each phase of matter has its own chemical and physical properties. The phases of matter you need to know are:
  • Solid - a solid has a definite shape and volume
  • Liquid - a liquid has a definite volume, but can change shape
  • Gas - the shape and volume of a gas can change
Phase Changes
These phases of matter can change from one to another. Remember the definitions of the following phase changes:
  • Melting - melting occurs when a substance changes from a solid to a liquid
  • Boiling - boiling is when a substance changes from a liquid to a gas
  • Condensing - condensation is when a gas changes to a liquid
  • Freezing - freezing is when a liquid changes to a solid
Physical & Chemical Changes
The changes that take place in substances may be categorized in two classes:
  • Physical Change - does not produce a new substance (e.g., phase changes, crushing a can)
  • Chemical Change - produces a new substance (e.g., burning, rusting, photosynthesis)