A chemical reaction occurs when two or more substances combine and the atoms are rearranged to create a new substance. A couple examples

There are at least 5 indicators that tell you a chemical reaction most likely occurred

A gas has been released this may result in fizzing or bubbles.

A change in odor like when you bake a cake or a foul smell.

A change in temperature this can be both getting hotter or colder.

Energy in the form of Light is produced this can be as simple as striking a match or a dramatic explosion.

A permanent change in color. For example, when you burn wood it changes from a light brown to black.

A precipitate is formed which just means a solid is formed. Or you could say “ a solid falls out of the solution.”