Difference Between Reactant and Reagent

Main Difference – Reactant vs Reagent

A chemical reaction involves the reaction between two or more compounds to make one or more new compounds. In other words, a chemical reaction is the change of reactants in order to form products. These reactants can be in solid phase, liquid phase or gaseous phase. The term reagent is used to describe a type of reactants. Reagents are added to a reaction mixture for the progression of the reaction. However, unlike reactants, reagents are not necessarily changed into some other compound. Thus, the main difference between reactant and reagent is that reactants are consumed in chemical reactions whereas reagents are not necessarily consumed during the progression of a reaction.  

Key Areas Covered

1. What is a Reactant
      – Definition, Explanation of Properties with Examples
2. What is a Reagent
      – Definition, Explanation of Properties with Examples
3. What is the Difference Between Reactant and Reagent
      – Comparison of Key Differences

Key Terms: Activation Energy, Indicator, Product, Reactant, Reagent

What is a Reactant

Reactants are the starting material that undergoes changes during a chemical reaction. Reactants are consumed in a chemical reaction. The chemical bonds in reactant compounds are broken in order to form new bonds, making a new compound. This new compound is called the product of the reaction.

The reactant molecules may be in solid, liquid or gaseous phase. Sometimes, reactants that are in different physical states may react with each other to form products. A chemical equation shows the reactants and product of a chemical reaction. A chemical equation uses an arrow to indicate the direction of the reaction from the arrow head. Reactants are on the left side of the arrow whereas products are on the right side.

When considering the kinetics of chemical reactions, the potential energy of products is determined by the type of reaction. If the reaction is an exothermic reaction, then the reactants are in a high energy level than that of products. If the reaction is endothermic, then the reactants are at a lower energy level than that of products. 

Figure 1: Exothermic and Endothermic Reactions

However, there are some elements and compounds that will never act as reactants due to their lack of reactivity. They are called inert compounds. But some elements and compounds may act as reactants under extreme conditions. For example, noble gases do not become reactants as they are completely stable at standard temperature and pressure conditions. But some of these noble gases can become reactants at extreme conditions. Ex: Xenon (Xe) can react with fluorine gas.

What is Reagent

A reagent is a compound that is added to a system in order to cause a chemical reaction. This reagent may or may not be consumed in the reaction. If it is consumed during the reaction, then that reagent is called a reactant. But sometimes reagents are used to initiate a reaction, to get a measurement of the reaction or to enhance a reaction. A reagent can be in solid or liquid phase before adding it to a reaction mixture.

For example, in acid-base reactions, indicator reagents are used to determine the end point of the reaction. This reagent gives a color change at the end point. Sometimes, catalyst reagents are used to enhance a chemical reaction. These catalysts can reduce the activation energy of reaction. 

There are reagents with specific names that are used for specific purposes. For example, Grignard reagent is used in the synthesis of aldehydes or ketones. Sometimes, the used reagent can be recovered after the completion of the reaction. But, the reagent is sometimes used by the reaction as a reactant. Then it cannot be recovered for further use.

Reagents are given an evaluation when they are produced. This is called the “reagent-grading”. This reagent grading indicates the purity of the reagent and where to use that reagent. Some reagents are stored in dark bottles. That is because these reagents are sensitive to the sunlight and can be cleaved in the presence of light. But other reagents are safe to be stored in transparent bottles.

Difference Between Reactant and Reagent

Definition

Reactant: Reactants are the starting materials that undergo changes during a chemical reaction.

Reagent: Reagents are the compounds that are added to a system in order to cause a chemical reaction.

Consumption

Reactant: Reactants are essentially consumed in chemical reactions.

Reagent: Reagents are not necessarily consumed in chemical reactions.

Application

Reactant: Reactants are used as the starting material for a chemical reaction.

Reagent:  Reagents are used to measure, enhance or initiate a chemical reaction.

Conclusion

The terms reactant and reagent are used interchangeably since reagents are sometimes consumed during a chemical reaction. But, reagents can be often distinguished from reactants according to their applications. However, the main difference between reactant and reagent is that reactants are consumed in chemical reactions whereas reagents are not necessarily consumed during the progression of a reaction. 

References:

1. “Reactants and Products in Chemical Reactions.” Dummies, Available here. Accessed 22 Aug. 2017.
2. Helmenstine, Anne Marie. “Here’s What a Reagent Is in Chemistry.” ThoughtCo, Available here. Accessed 22 Aug. 2017.

Image Courtesy:

1. “Figure 06 03 03” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Colored pH indicator (circle)” By TheChimist – Own work (CC BY-SA 4.0) via Commons Wikimedia