What evidence must be present to indicate a chemical or physical change?

While physical change is the rearranging of molecules in a substance, a chemical change affects the intrinsic properties of a substance, altering its chemical composition.

In order for a chemical change to have occurred, a new substance must be formed. Physical changes can be undone, such as the freezing of water, while chemical changes cannot be undone; a chemical change causes the substance to change into another, different substance. Some physical changes include changes in texture, color, temperature and state. Some signs that a chemical change has occurred include presence of odor, formation of a precipitate, rusting of iron and the formation of bubbles.