Question

(a) What is the difference between displacement and double displacement reaction? Write equations for these reactions.

(b) Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
[ 5 Marks]

Answer 1

(a) In a displacement reaction, a more reactive element displaces a less reactive element from its compound or salt solution.
In a double displacement reaction, two compounds react by exchanging their ions to form new compounds. It is typically identified by the formation of a product that is a precipitate.
[1 Mark]
Example for displacement reaction:
${\text{CuSO}}_4\text{(aq)}+\text{Zn(s)}\to {\text{ZnSO}}_4\text{(aq)}+\text{Cu(s)}$
[0.5 Marks]
Example for double displacement reaction:
${\text{Na}}_2{\text{SO}}_4\text{(aq)}+{\text{BaCl}}_2\text{(aq)}\to {\text{BaSO}}_4\text{(s)}+2\text{NaCl(aq})$
[0.5 Marks]


(b) In the presence of heat (Thermal decomposition reaction):
${\text{CaCO}}_3\text{(s)}\to \text{CaO(s)}+{\text{CO}}_2\text{(g)}$
[1 Mark]

In the presence of sunlight (Photolytic decomposition reaction):
$2\text{AgCl(s)}\to 2\text{Ag(s)}+{\text{Cl}}_2\text{(g)}$
[1 Mark]
In the presence of electricity (Electrolytic decomposition reaction):
$2{\text{H}}_2\text{O(l)}\to 2{\text{H}}_2\text{(g)}+{\text{O}}_2\text{(g)}$
[1 Mark]