Evidences of chemical change

• formation of gas
• formation of a precipitate (insoluble solid)
• unexpected change in color
• unexpected change in odor

• release of heat energy
• release of light
• production of sound
• unexpected change in temperature
• absorption or release of electrical energy

Pure substances are composed of the same kind of matter, they are either elements or compounds.

A chemical change is a change in which the composition of the substance is altered.

Review

Chemical Reactions