Understanding Limiting Reagents and How They Are Used

The chemical reactant or reagent that tells us about the quantity or concentration of the products produced in a reaction is known as the limiting reagent. Since some excess amounts of the other reactants remain in the solution after the limiting reactants are completely consumed, they are often called excess reactants. 

This amount of product, also known as theoretical yield, produces the most amount of product. To calculate a percentage yield from a chemical process, the limiting reagent must be identified.

Identifying the limiting reagent, estimating the excess quantities of other reagents, and computing the quantity of each reagent based on the balanced chemical equation that describes the reaction are all equivalent techniques. 

We will have a better knowledge of what a limiting agent is, how to identify limiting reagents, and a few queries concerning limiting agents after reading this article. 

Limiting Reagent – What is it? 

In most cases, this reactant dictates when the reaction will come to a halt. The reaction stoichiometry may be used to compute the precise quantity of reactant required to react with another element. The mole ratio, not the masses of the reactants present, determines the limiting reagent. 

The limiting reactant, which can be seen, is the reason the reaction can’t go on since there’s nothing left to react with the excess reactant. It is the reactant that is completely consumed throughout the reaction.

When this reactant is present, the reaction usually stops. From the reaction, stoichiometry can calculate the exact concentration of reactant required to react with another element. Reactants present in the reaction have different masses, so the limiting reagent depends on their mole ratio and not on their masses. 

The reactants are expected to appear in ratio otherwise the reaction will be limited by one. One of the methods to determine the limiting reagent is to search and make a comparison of the mole ratio of reactants. Another way to determine is to calculate the mass of products generated from specified quantities.

In order to understand how ammonia is formed, let us consider the following reaction:

3H2+N2 —> 2NH3

in order To form 2 moles of ammonia, the hydrogen gas is reacted with 1 mole of nitrogen gas in a reaction shown above. What happens, however, if two moles of hydrogen gas are available with one mole of nitrogen at the time of the reaction?

Regardless of the quantity of nitrogen, the entire quantity of hydrogen gas cannot be used since the whole quantity of nitrogen requires 3 moles to react. In consequence, hydrogen gas is a limiting agent in the reaction and is referred to as the limiting agent.

Let us look at an example 

Here is the important chemical equation representing benzene combustion:

2C6H6(l)+15O2(g) —> 12CO2(g)+6HO2(l)

It means that 15 moles of molecular oxygen O2 are needed to react with 2 moles of benzene C6H6. 

Cross-multiplication is used to calculate the amount of oxygen required for other quantities of benzene. For example, if 1.5 mol C6H6 is present, 11.25 mol O2 is required:

1.5 mol C6H6 x 15 mol O2 / 2 mol C6H6

= 11.25 mol O2 

If 18 mol O2 are present, there would be an excess of (18 – 11.25) = 6.75 mol of unreacted oxygen when all of the benzene is consumed. therefore Benzene is the limiting reagent.

How Do I Find a Reaction’s Limiting Reagent?

Let’s look at some reactions now that we know how to find the limiting reagents.

There are two methods for determining the limiting reagent. One technique to figure out which one is the most effective is to compare the mole ratios of the reactants.

You may compute the grammes of products created from the amounts of reactants by utilising the reactant that creates the least quantity of product as the limiting reagent.

Method 1: To identify the limiting reagent, determine the quantity of each reactant in moles.

  1. For the given reaction, find the balanced chemical equation.
  2. Determine the molecular mass of all of the data (using the molar mass as a conversion factor).
  3. We can determine the mole ratio using the information provided. Compare the computed ratio to the actual ratio to see if the ratio is correct.
  4. Calculate the quantity of product created using the amount of limiting reactant.
  5. Determine how much more non-limiting agent is left, if necessary.

Method 2: To discover the limiting reagent, calculate and compare the quantity or concentration of product each reactant would create.

  1. Balancing the chemical equation for the given chemical reaction is the first step.
  2. After that, transform the supplied data into moles.
  3. Determine the mass of the product created using stoichiometry for each individual reactant.
  4. The limiting reagent is the reactant or reagent that creates the least quantity of product.
  5. The excess reagent would be the reactant that creates the most product.
  6. To calculate the quantity of excess reagent left, subtract the total mass of excess reagent eaten from the amount of surplus reagent delivered.

Why is the limiting reactant important?

Using the limiting reactant/reagent makes it possible for chemists to determine only x moles of compounds can form when the perfect quantity is used with the amount they must use of this material because it relates to the actual reaction instead of assuming that it may happen.

Does a limiting reagent or reactant provide any benefit in this?

Chemical reactions require the use of limited reagents or reactants. This technique facilitates predicting the maximum amount of reactant to be consumed because it limits the reaction, at the end of which only the necessary volume of products can be produced rather than the hypothetical yield produced by perfect quantities.


Limiting reactants (or limiting reagents) are the reactants that get consumed first in a chemical reaction, thereby limiting the amount of product that can be produced. The limiting reactant can be determined in many ways, but they all use mole ratios from a balanced chemical equation.

The theoretical yield is the quantity of product that can be created based on the limiting reactant. Because the product is really gathered rather than theoretically collected, the actual yield is substantially lower than the theoretical yield. Percentage yields are often represented as a percentage of theoretical yields.