What is a Displacement Reaction? (Definition and Examples)

A Displacement Reaction (or Single Displacement Reaction) is a chemical reaction in which a more highly reactive element displaces (kicks out and replaces) a less reactive element from its aqueous salt solution.

• General Formula: $A + BC \rightarrow AC + B$ (Here, element A is more powerful/reactive than element B, so it takes B's place).

The most famous textbook example involves putting an iron nail into a blue solution of Copper Sulphate.

• Reaction: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$
• What happens: Iron (Fe) is situated higher on the Reactivity Series than Copper (Cu). Therefore, Iron kicks the Copper out of the solution. The blue color of the solution slowly fades to light green (Iron Sulphate), and a brown coating of pure copper metal forms over the iron nail.

There is a second variation called a Double Displacement Reaction. In this, two different compounds completely exchange their ions to form two new compounds. This usually results in the formation of a solid precipitate.

• Example: $Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) \downarrow + 2NaCl(aq)$