2. Chemical Equations

Look at this rusty bike wheel. It has been left outside in damp weather too many times, so the iron in the metal parts has rusted. Iron rusts when it combines with oxygen in the air. Iron rusting is an example of a chemical reaction. In a chemical reaction, substances change into entirely different substances. For example, the iron in the bike and the oxygen in the air have changed into rust. How could you represent this reaction, besides just describing it in words? Scientists use a standard method to represent a chemical reaction, called a chemical equation.

What Is a Chemical Equation?

A chemical equation is a shorthand way to sum up what occurs in a chemical reaction. The general form of a chemical equation is:

                Reactants → Products

The reactants in a chemical equation are the substances that begin the reaction, and the products are the substances that are produced in the reaction. The reactants are always written on the left side of the equation and the products on the right. The arrow pointing from left to right shows that the reactants change into the products during the reaction. 

The general equation for the reaction in which iron rusts is shown below as an example: 

Iron + Oxygen → Iron Oxide

Using Chemical Symbols and Formulas

When scientists write chemical equations, they use chemical symbols and chemical formulas instead of names to represent reactants and products. Look at the chemical reaction illustrated below. In this reaction, carbon reacts with oxygen to produce carbon dioxide. Carbon is represented by the chemical symbol C. The chemical symbol for oxygen is O, but pure oxygen exists as diatomic (“two-atom”) molecules, represented by the chemical formula O2. A molecule of the compound carbon dioxide consists of one atom of carbon and two atoms of oxygen, so carbon dioxide is represented by the chemical formula CO2.

The chemical equation for this reaction is:

C + O2 → CO2