Science, Tech, Math › Science Reagent Definition and Examples What Is a Reagent in Chemistry? Share Flipboard Email Print Westend61/Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 07, 2019 A reagent is a compound or mixture added to a system to cause a chemical reaction or test if a reaction occurs. A reagent may be used to find out whether or not a specific chemical substance is present by causing a reaction to occur with it. Reagent Examples Reagents may be compounds or mixtures. In organic chemistry, most are small organic molecules or inorganic compounds. Examples of reagents include Grignard reagent, Tollens' reagent, Fehling's reagent, Collins reagent, and Fenton's reagent. However, a substance may be used as a reagent without having the word "reagent" in its name. Reagent Versus Reactant The term reagent is often used in place of reactant, however, a reagent may not necessarily be consumed in a reaction as a reactant would be. For example, a catalyst is a reagent but is not consumed in the reaction. A solvent often is involved in a chemical reaction but it's considered a reagent, not a reactant. What Reagent-Grade Means When purchasing chemicals, you may see them identified as "reagent-grade." What this means is that the substance is sufficiently pure to be used for physical testing, chemical analysis, or for chemical reactions that require pure chemicals. The standards required for a chemical to meet reagent-grade quality are determined by the American Chemical Society (ACS) and ASTM International, among others.