Reagent Definition and Examples

What Is a Reagent in Chemistry?

A reagent is a substance that is used in chemical analysis and to synthesize other products.
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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 tell 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 in its name.

Reagent Versus Reactant

The term reagent is often used in place of reactant, but a reagent may not necessarily be consumed in a reaction like a reactant. For example, a catalyst is a reagent but is not consumed in the reaction. A solvent often is involved in a chemical reaction — it is considered a reagent, but 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 that it may 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.