In a chemical equation, what are reactants?

In a chemical equation, reactants are the substances that undergo change during a chemical reaction. This means that they are the starting materials that react with one another to form products. When a chemical reaction occurs, the bonds between atoms in the reactants are broken, rearranged, and reformed to create new substances. This fundamental concept is crucial in understanding chemical reactions, as it highlights the transformation of matter that occurs in these processes.

The other concepts described in the other choices clarify different aspects of chemical reactions but do not define reactants. For example, substances that remain unchanged during a reaction are not involved in the transformation that characterizes reactants. Similarly, substances produced after the reaction are known as products, and substances that catalyze a reaction facilitate it without being consumed in the process. Understanding the role of reactants in chemical equations is essential for studying how reactions proceed and how different substances interact at the molecular level.