Editing Reagent (section)

{{short description|Substance added to a system to cause a chemical reaction}}
{{distinguish|Regent}}
{{redirect-distinguish|Reactants|Reactance (disambiguation){{!}}Reactance}}
[[File:SulfurReagent.jpg|thumb|Reagents, such as [[sulfur]] (pictured), are the starting materials used in chemical reactions.]]

In [[chemistry]], a '''reagent''' ({{IPAc-en|r|i|ˈ|eɪ|dʒ|ən|t}} {{respell|ree|AY|jənt}}) or '''analytical reagent''' is a substance or compound added to a system to cause a [[chemical reaction]], or test if one occurs.<ref name=gold>{{GoldBookRef |title=Reactant |file=R05163 |year=1996}}</ref> The terms ''reactant'' and ''reagent'' are often used interchangeably, but '''reactant''' specifies a substance ''consumed'' in the course of a chemical reaction.<ref name=gold/> ''[[Solvent]]s'', though involved in the [[reaction mechanism]], are usually not called reactants. Similarly, ''[[catalysis|catalysts]]'' are not consumed by the reaction, so they are not reactants. In [[biochemistry]], especially in connection with [[enzyme]]-catalyzed reactions, the reactants are commonly called [[substrate (biochemistry)|substrates]].