In a chemical reaction, reactants are the substances that undergo a change to form new substances, known as products. They are found on the left side of a chemical equation. During the reaction, the bonds in the reactants break, allowing the atoms to rearrange and form new bonds to create the products. For example, in the equation for the combustion of methane:
\[ \text{CH}_4 + 2 \text{O}_2 \rightarrow \text{CO}_2 + 2 \text{H}_2\text{O} \]
The reactants are methane (\( \text{CH}_4 \)) and oxygen (\( \text{O}_2 \)), while the products are carbon dioxide (\( \text{CO}_2 \)) and water (\( \text{H}_2\text{O} \)).