2.3 Chemical Properties and Reactions

Chemical Reactions

When one or more elements and compounds are changed into another set of elements or compounds, a chemical reaction has taken place. In a chemical reaction, the substances you start with are called the reactants. The substances into which they change are called the products. Reactants and products can be either elements or compounds. The bonds between the reactants are broken and reformed during a chemical reaction. Common chemical reactions include oxidation (burning and rusting), in which a substance combines with oxygen, and digestion, in which foods are broken down by stomach acids into nutrients the body can use.

A second key characteristic of chemical reactions is that matter is neither created nor destroyed. It simply changes from one form to another. Therefore, the total mass of the reactants equals the total mass of the products. If you found the mass of the reactants before the reaction and the mass of the products after the reaction, the masses would be the same. This principle is called the Law of Conservation of Matter.