Because, in Double Displacement Reaction, reactants mutually exchange their ions in two compounds to form the new products.
Examples :-(i) Na2SO4 + BaCl2 ––> BaSO4 + NaCl
(ii) BaCl2 + H2SO4 ––> BaSO4 + HCl.

Here, in example (i), Sodium Sulphate and Barium Chloride are the two compounds. Sodium Sulphate reacts Barium Chloride by mutually exchanging their ions to form Sodium Chloride and Barium Sulphate. In the place of Sodium Sulphate, Sodium Chloride is formed and in the place of Barium Chloride, Barium Sulphate is formed. In this reaction, Chlorine and Sulphate are the ions where the ions get transfer to the two compounds by mutually exchanging their ions in two compounds.

Double Displacement Reaction:

Double displacement reaction is a chemical reaction that involves the exchange of ions or atoms between two compounds. It is also known as metathesis reaction. The reaction takes place between two ionic compounds and results in the formation of two new compounds.

Naming of Double Displacement Reaction:

The double displacement reaction is named so because during the reaction, two compounds exchange their ions or atoms with each other, resulting in the formation of two new compounds. The reactants and products of the reaction have the same cations and anions but are arranged differently.

Example:

An example of a double displacement reaction is the reaction between Sodium Hydroxide (NaOH) and Hydrochloric acid (HCl) to form Sodium Chloride (NaCl) and Water (H2O).

NaOH + HCl → NaCl + H2O

In this reaction, the Sodium Ion (Na+) from Sodium Hydroxide and the Chloride Ion (Cl-) from Hydrochloric acid form Sodium Chloride (NaCl), while the Hydroxide Ion (OH-) from Sodium Hydroxide and the Hydrogen Ion (H+) from Hydrochloric acid form Water (H2O).

Explanation:

The reaction can be explained using the following points:

- Sodium Hydroxide (NaOH) is a strong base, while Hydrochloric acid (HCl) is a strong acid.
- When Sodium Hydroxide reacts with Hydrochloric acid, the Hydroxide Ion (OH-) from Sodium Hydroxide reacts with the Hydrogen Ion (H+) from Hydrochloric acid to form Water (H2O).
- The Sodium Ion (Na+) from Sodium Hydroxide and the Chloride Ion (Cl-) from Hydrochloric acid combine to form Sodium Chloride (NaCl).
- The reaction is a double displacement reaction because the cations and anions of two compounds exchange their positions to form two new compounds.
- The reaction is also a neutralization reaction because a strong acid and a strong base react to form a salt and water.

Conclusion:

Double displacement reaction is a type of chemical reaction where two ionic compounds exchange ions or atoms with each other to form two new compounds. The reaction is named so because the reactants and products have the same cations and anions but are arranged differently. An example of a double displacement reaction is the reaction between Sodium Hydroxide and Hydrochloric acid to form Sodium Chloride and Water.