Chemical Reactions

Chemical decomposition can occur in the following cases

Case-i: A compound decomposes into two elements

Example: When electric current is passed through acidified water, it decomposes to give hydrogen gas and oxygen gas. This is known as electrolysis and the reaction is called as electrolytic decomposition reaction.It can be represented as :
        2H₂O(l)    \( \to \)     2H₂ (g)    +      O₂ (g)
        Water    \( \to \)      Hydrogen    +    Oxygen

Case-ii: A chemical compound decomposes into two compounds.

Example: When calcium carbonate is heated, it decomposes to give calcium oxide
and carbon dioxideThis reaction can be called as thermal decomposition reaction as
the energy is supplied in the form of heat.The equation is represented as:
    CaCO₃(s)            \( \to \)                    CaO(s)     +       CO₂(g)
    Calcium carbonate       \( \to \)     Calcium oxide   +  Carbon dioxide
    (Limestone)                             (Lime)

Chemical decomposition reactions are generally endothermic reactions.That is, they require energy in the form of heat,light or electricity.But,all decomposition reactions are not endothermic,they can be exothermic either.(exothermic reactions involve release of energy).

For example the decomposition of ozone to form dioxygen and oxygen radical is an exothermic reaction.The equation is represented as: 

 O₃   +hv(light energy)    \( \to \)     O₂          +      O*.
                   ozone                dioxygen +  oxygen radica

we can observe that the decomposition of ozone is using light energy.so we can call this reaction as  photo decomposition/photoplytic decomposition/photochemical decomposition reaction

SOME USES OF DECOMPOSITION REACTIONS
-In manufacture of cement amnd calcium oxide
-In extraction of metals(metallurgical processes).
-In relief from acid indigestion.
-In thermite welding.