What does reactant mean?
A reactant is a substance that participates in a chemical reaction and undergoes a chemical change. In an equation, reactants appear on the left side of the arrow, while products appear on the right. The distinction matters because some reactions can proceed only until one reactant is exhausted; this is called the limiting reactant, and its amount often determines how much product can be made. Reactants may be elements or compounds, and they can react in many different proportions depending on the chemical process involved. The term also appears in biochemistry, where substances such as enzymes and other molecules interact in complex reaction pathways. In everyday writing, reactant is uncommon because it has a precise technical meaning rather than serving as a general term for anything that participates in an event. Using it accurately helps distinguish substances that are transformed during a reaction from those that merely enable the reaction to occur.
nounA substance that takes part in a chemical reaction and is chemically altered in the process.
- A substance that takes part in a chemical reaction and is chemically altered in the process.
"The limiting reactant determines how much of the desired product can form."
"The reactants were mixed in a sealed flask under carefully controlled temperatures."
"In this biochemical reaction, the enzyme helps the reactants combine more efficiently."
The standard plural form, especially common when referring collectively to the substances involved in a reaction.
"The reactants react at different rates, so the mixture changes composition over time."
The limiting reactant is the reaction's bottleneck: once it runs out, production of the corresponding product stops.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does reactant come from?
Reactant was formed in English from react plus the suffix -ant, meaning a person or thing that performs or undergoes an action. React comes from Latin reagere, literally “to drive back” or “return,” and is built on the Latin root agere, “to do” or “act.” Words such as reaction, reactive, and reactor belong to the same English family, while action and active derive from the same Latin root.
Related word forms
How reactant is actually used
Chiefly used in chemistry and related technical writing. Outside scientific contexts, the word is uncommon and is not normally a general synonym for an ingredient or participant.
Easily confused with reactant
A reagent is a substance used to bring about a chemical reaction, whereas a reactant is a substance that participates in the reaction and is chemically transformed.