What is meant by (a) displacement reaction, and (b) double displacement reaction? Explain with the help of one example each.
(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.
Example: CuSO4 (aq) + Zn (s) → ZnSO4 + Cu
When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained. In this reaction, zinc displaces copper from copper sulphate compound so that copper is set free. The blue colour of copper sulphate solution fades due to the formation of zinc sulphate.
(b) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.
Example: AgNO3 (aq) + NaCl (aq)
When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed along with sodium nitrate solution. In this reaction, two compounds, silver nitrate and sodium chloride, react to form two new compounds, silver chloride and sodium nitrate.