Limiting Reagent

In any chemical process, the limiting reactant (or reagent) is a material which is totally absorbed when the chemical reaction is complete.

This reagent restricts the amount of the product created and the reaction cannot continue without it. 

During the precipitation reaction, information regarding the limiting agent can be determined by the presence of partial precipitation. 

In dissolving reactions, limiting reactants can be formed by the clear saturated or unsaturated solution.

In the gaseous reaction by measuring the mixture of gases that are generated can identify the limiting reagent.

In most circumstances, this reactant dictates when the reaction will come to a finish.

Because of the stoichiometry of the reaction, it is possible to determine the exact quantity of reactant that will be required to react with a different element. 

However, rather than the quantities of the reactants present, the mole ratio of the reactants determines which limiting reagent is used.

The reaction cannot proceed since there is nothing available to combine with the excess reactant after the limiting reactant has been consumed. 

Identification Of Limiting Reagent

The procedure to identify the limiting reagent is as follows:-

If the chemical formula is not balanced, make the necessary adjustments.

Figure out how many moles of each reactant there were in total during the reaction.

Check to see what the overall number of products produced is during the reaction.

Calculate which of the reactants produces the smallest amount of products; this is referred to as the limiting agent.

Limiting reagents are the chemicals that are entirely consumed in the completion of a chemical reaction.

They are also referred to as limiting agents or limiting reactants.

 According to the stoichiometry of chemical reactions, a predetermined amount of reactants is required for the completion of the reaction.

Consider the following reaction that results in the creation of ammonia:-

   3H2+ N2→ 2NH3

Specifically, in the reaction described above, three moles of hydrogen gas must react with one mole of nitrogen gas in order to produce two moles of ammonia. 

But what happens if, during the reaction, only 2 moles of hydrogen gas and 1 mole of nitrogen are accessible at the same time is that the complete amount of nitrogen is unable to be utilised (because the entirety of nitrogen requires 3 moles of hydrogen gas to react).

Because the hydrogen gas is restricting the reaction, it has been designated as the limiting reagent for this reaction.

Examples

Consider the burning of benzene, which can be represented by the chemical equation below:

6 HO2 + 12 CO2 = 2C6H6(l) + 15 O2(g) = 12 CO2(g) + 6 HO2 (l)

To put it another way, for every mole of benzene C6H6 that is consumed, 15 moles of molecular oxygen O2 must be consumed. 

Cross-multiplication is used to determine the quantity of oxygen that is necessary for the production of other quantities of benzene.

For example, if 1.5 mol of C6H6 is present, 11.25 mol of oxygen is required to complete the reaction:

1.5 mol C6H6 * (15mol O2/ 2molC6H6) = 11.25 mol of O2

Assuming that there are 18 mol O2 in the mixture, there will be an excess of (18 – 11.25) = 6.75 mol of unreacted oxygen after all the benzene has been consumed. As a result, benzene serves as the limiting reagent.

Conclusion

When a chemical reaction is finished, the limiting reagent (also known as the limiting reactant or the limiting agent) is a reactant that has been completely consumed by the chemical reaction.

This reagent has a limit on the amount of product that can be generated because the reaction cannot proceed if it is not present. 

Because the theoretical yield is defined as the amount of product obtained when the limiting reagent reacts entirely, it is necessary to identify the limiting reagent before calculating the percentage yield of a reaction. 

Given the balanced chemical equation that describes the reaction, there are multiple similar methods for identifying the limiting reagent and determining the excess quantities of other reagents present in the mixture.