A
reagent is a substance or compound added to a system to cause a chemical reaction, or added to see if a reaction occurs. The terms
reactant and
reagent are often used interchangeably—however, a
reactant is more specifically a substance consumed in the course of a chemical reaction.
Solvents, though involved in the reaction, are usually not called reactants. Similarly,
catalysts are not consumed by the reaction, so are not reactants.