Chemical reaction is the process in which one or more substances, the reactants, are transformed into one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products. Although the identities of the atoms are preserved, some of the physical properties of the reactants may differ from those of the products. For instance, the reactants may be solids, while the products are gaseous or liquid, and vice versa.

Chemical reactions can be classified as either complete, partial, or stoichiometric. A complete chemical reaction is a reaction in which one or more reactants are entirely converted into products. A partial chemical reaction is a reaction in which one or more reactants are partially converted into products, and some reactants remain unchanged. A stoichiometric chemical reaction is a reaction in which the reactants are present in exactly the right proportions, so that all of the reactants are entirely consumed, and no reactants remain unchanged.

The chemical change in the chemical reaction can be determined by observing the following physical changes:

- Change in color

- Evolution of gas

- Formation of a precipitate

- Change in temperature