Which term describes a chemical substance present at the start of a chemical reaction?

The term that describes a chemical substance present at the start of a chemical reaction is "reactant." Reactants are the starting materials that undergo a transformation during the chemical process. During the reaction, reactants interact with each other to form new substances known as products.

In a chemical equation, reactants are typically listed on the left side, while products are shown on the right side. Understanding the role of reactants is fundamental in the study of chemical reactions, as they provide the necessary components for the reaction to occur.

Products, on the other hand, are the substances that form as a result of the reaction. A catalyst is a substance that speeds up a chemical reaction without being consumed in the process, while an intermediary refers to a substance formed during the steps of the reaction and would not be present at the start. Therefore, "reactant" accurately reflects the substances involved at the initiation of a chemical reaction.