Let us make an attempt to know two important and basic concepts of chemistry.

In a chemical reaction, it is essential to know the participating reactants and the resultant. The resultant varies according to the proportion of the reactants along with various internal and external conditions. In a chemical reaction when the substance is totally consumed it is referred to as a limiting reagent. Limiting reagent is also know as a limiting agent or limiting reactant.

Limiting reagent is responsible for limiting the quantity of the product produced and is the main element of the chemical reaction. In a precipitation reaction, the incomplete precipitation gives the idea of limiting reagent. In dissolution reaction, the clear unsaturated or saturated solution produces the limiting reactant. In a gaseous reaction, the limiting reagent is found by analyzing the mixture of gases that are produced.

If one or more reagents are present in excess, to react with the limiting reagent, they are known as excess reactants or excess reagents.

How To Calculate Limiting Reagent

Steps to calculate the limiting reagent:

  • First, balance the chemical equation or check if the reaction is balanced.
  • Find the number of moles of every reactant in the reaction.
  • Calculate the number of products that are formed after the chemical reaction.
  • Determine the reactant which produced the minimum quantity of the product and hence the limiting reagent is found.


Find the limiting reactant in an aluminum wire which weighs 54g and is dipped in 2 L of 1M sulfuric acid. The atomic mass of Al is 27.

Balancing the chemical reaction:

From the reaction, we can find that 2 molecules of Al require 3 moles of H2SO4

54 g of Al = 54/27 = 2 molecules

Hence 3 moles of is needed.

We have 2L of 1M which equals 2 moles

Hence we can conclude that Sulfuric acid is the limiting reactant in the reaction.

Now let us understand the molecular orbital theory.

A molecular orbital is produced when the atomic orbitals overlap with each other to form new orbitals. The molecular orbital theory is a technique explained in the twentieth century by R. S. Mulliken and F. Hund to describe the structure and properties of different molecules. This theory gives a method of understanding the structure of a molecule by using molecular orbitals of the atoms.

As we know in the method of forming the molecule, the atoms combine with each other. The number of orbitals present in the molecule is directly equal to the number of orbitals present in the combining atoms. When 2 atoms combine with each other having one atomic orbital, 2 molecular orbitals are produced.

Molecular orbital theory can be demonstrated by analyzing molecules of compounds like H and He which are diatomic in nature. The energy level representation is as shown below in the figure. Here each atom of hydrogen features one 1s electron. In the H 2 molecule, the 2 hydrogen electrons occupy the lowest energy level in the molecular orbital, the sigma orbital

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