A chemical change is when matter converts from one type to another type. Some examples of chemical changes:

• Formation of rust: Rust is a different kind of matter than the iron, oxygen, and water present before the rust formed.
• The explosion of nitroglycerin: Gases produced are very different kinds of matter from the original substance.
• All form of combustion
• Food is cooked, digested, or rotting.

A physical change is a change in the form of a substance but not its composition. It occurs when matter changes among solid, liquid, or gaseous states. You can see a physical change when you freeze or boils water. The water turns states, but it is still composed of H₂O molecules.

During chemical change or physical changes, there is no detectable change in the total quantity of matter. This phenomenon is called the law of conservation of matter.