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Reactant vs. Reagent: What's the Difference?

Edited by Janet White || By Harlon Moss || Published on November 11, 2023
A reactant is a substance consumed in a chemical reaction, while a reagent is a substance used to detect or measure another substance.

Key Differences

Reactant and reagent are both terms associated with chemical reactions, but they serve different roles. A reactant is a starting material in a chemical reaction that undergoes a change to produce a new substance. For example, in the combustion of methane, methane is a reactant that reacts with oxygen to produce carbon dioxide and water.
On the other hand, a reagent is a substance introduced to a system to bring about a chemical reaction or to test for the presence of another substance. For instance, in chemical tests for glucose, Benedict's solution serves as a reagent to detect the sugar's presence. While every reactant is involved directly in the formation of products, a reagent might not necessarily be a part of the final products.
While both reactants and reagents play critical roles in chemical reactions, their purposes are distinct. Reactants are the focus of transformation, becoming products as the reaction progresses. Reagents, however, facilitate or indicate reactions, often used in laboratory settings to test or initiate reactions without always becoming part of the result.
The terms can sometimes be confusing as some substances can act as both a reactant and a reagent, depending on the context. For example, hydrogen peroxide can be a reactant when it decomposes into water and oxygen. Still, it can also act as a reagent when used to test for the presence of certain enzymes. Understanding the distinct roles each plays in chemical reactions is essential for accurate scientific communication.

Comparison Chart


A substance consumed in a chemical reaction.
A substance used to initiate, detect, or measure another substance.


Undergoes change to become a product.
Facilitates or indicates a reaction.

Presence in End Product

Does not remain in its original form.
Might not necessarily become part of the product.


Always part of the initial components in a chemical reaction.
Often introduced to test for another substance or initiate a reaction.


Hydrogen and oxygen are reactants in the formation of water.
Benedict's solution is a reagent to test for glucose.

Reactant and Reagent Definitions


A substance that undergoes change in a chemical reaction.
In the reaction, methane is a reactant that burns to form water and carbon dioxide.


A compound used to initiate a chemical reaction.
The reagent triggered a rapid color change in the solution.


An initial component in a chemical equation.
The left side of the equation lists all the reactants.


A substance introduced to cause or test for a reaction.
The chemist added a reagent to detect the presence of chloride ions.


A starting material in a chemical process.
Oxygen is a common reactant in combustion reactions.


A chemical solution used for identification or analysis purposes.
The lab technician employed a specific reagent to confirm the substance's identity.


A compound that participates directly in the formation of products.
In photosynthesis, carbon dioxide is a key reactant.


An agent used in labs to detect or measure another substance.
Bromine water is a reagent used to test for unsaturated hydrocarbons.


An ingredient that gets transformed during a reaction.
Acid is a reactant when neutralized by a base.


A material that might not become part of the final product in a reaction.
The reagent was used to start the reaction, but it was not found in the end product.


A substance that is altered or incorporated into another substance in a chemical reaction, especially a directly reacting substance present at the initiation of the reaction.


A substance used in a chemical reaction to detect, measure, examine, or produce other substances.


(chemistry) Any of the participants present at the start of a chemical reaction, specifically one that is consumed during the reaction.


(chemistry) A compound or mixture of compounds used to treat or test materials, samples, other compounds or reactants in a laboratory or sometimes an industrial setting.


A chemical substance that is present at the start of a chemical reaction


A substance capable of producing with another a reaction, especially when employed to detect the presence of other bodies; a test.


A chemical agent for use in chemical reactions


What's the primary difference between a reactant and a reagent?

A reactant is consumed in a reaction, while a reagent facilitates or indicates a reaction.

Why are reagents important in laboratory tests?

Reagents help detect, initiate, or measure reactions, often without becoming part of the final result.

Can a substance be both a reactant and a reagent?

Yes, depending on the context, a substance can act as both.

Can a reaction have multiple reactants?

Yes, many reactions involve more than one reactant.

Is a reactant present in the final product of a reaction?

A reactant undergoes change and does not remain in its original form in the product.

Do reagents always participate in reactions?

Reagents facilitate or indicate reactions but might not always participate in the formation of the end product.

What determines if a substance is a reactant or a reagent?

Its role in the reaction – if it's consumed, it's a reactant; if it facilitates or indicates, it's a reagent.

Are reagents always safe to handle?

No, some reagents can be toxic or corrosive and require caution.

In what field is the term "reagent" most commonly used?

Reagent is frequently used in chemistry, especially in laboratory settings.

Do all reactions need a reagent?

No, not all reactions require a reagent.

Can the absence of a reactant halt a reaction?

Yes, if a necessary reactant is missing, the reaction might not proceed.

Can a reagent be reused?

Some reagents can be recovered and reused, while others cannot.

Are reactants always liquids?

No, reactants can be solids, liquids, or gases.

Is the amount of reactant important for a reaction?

Yes, the quantity of reactant can determine the yield and rate of a reaction.

Can a reagent be considered a catalyst?

While both can initiate reactions, a catalyst speeds up a reaction without being consumed, while a reagent may or may not be consumed.

Is every substance added to a reaction a reagent?

Not necessarily, only substances added to initiate, detect, or measure are reagents.

Can you predict the products of a reaction from its reactants?

Often, yes, but sometimes reactions can have unexpected products.

Are the terms reactant and reagent interchangeable?

No, they have distinct roles in chemical reactions.

Why is it crucial to differentiate between reactants and reagents?

Proper differentiation ensures accurate scientific communication and understanding.

Are reactants always on the left side of a chemical equation?

Typically, yes. Reactants are listed on the left, with products on the right.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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