A displacement reaction is a reaction in which an atom, or a group of atoms, present in a molecule is displaced by another atom. For example, iron when added to a solution of copper sulphate displaces copper metal.
Dissolve 0.5 g of Silver nitrate in 10 ml water in a test tube. Place a clean copper wire in the test tube. Keep it for some time. Shining crystals of silver appear on the Copper wire. The colour of the solution becomes bluish as some copper nitrate is formed.
In this reaction, copper metal has displaced silver from the solution of silver nitrate.
Dissolve 5 g of copper sulphate in 100 ml water. Place the copper sulphate solution in three different beakers. In one beaker put 5g of magnesium metal, in the second put 5g of zinc metal and add 5g of iron into the third beaker and keep it for some time.
After some time the blue colour of the solution fades and red coloured copper metal is displaced from the copper sulphate solution. The displacement reactions which occur are:
Mg(s) + CuSO4(aq) MgSO4(aq) + Cu(s)
Zn(s) + ZnSO4(aq) ZnSO4(aq) + Cu(s)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
Some other examples of displacement reactions are:
2Na + 2H2O 2NaOH + H2
2Al + Fe2O3 Al2O3 + 2Fe
2KI + Cl2 2KCl + I2