In a chemical change or reaction, the original substances' chemical composition is changed. You cannot get back your original substances. This would be like un-baking a cake.

Watch the following video to learn about the evidences of chemical reactions.

Some signs (or evidence) of chemical change are

• production of a gas (bubble formation),
• change in temperature,
• formation of a precipitate (a solid),
• change in color, and
• production of a new odor.

Watch the following two videos, and use your notes to list the evidences of a chemical reaction that you see.