A reagent or reactant's a substance or compound consumed during a chemical reaction. Solvents and catalysts, although they're involved in the reaction, are usually not referred to as reactants. Although the terms reactant and reagent are often used interchangeably, a reagent's more specifically "a test substance that's added to a system in order to bring about a reaction or to see whether a reaction occurs". Such a reaction's used to confirm the presence of another substance. Examples of such a… (More on Reactant)