A reagent or reactant is 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, reagent is often used in a more specialized sense as "a test substance that's added to a system in order to bring about a reaction or to see whether a reaction occurs". Examples of such analytical reagents include Fehling's reagent a… (More on Reactant)