Decomposition reactions are the reactions where a reactant breaks down into two or more products.

a. Decomposition by heat:

Ferrous sulphate decomposes to give ferrous oxide, sulphur dioxide and sulphur trioxide as,

\[
2FeSO_4{}_{\mathrm{(s)}}
\mathrel{\mathop{\longrightarrow}^{\Delta}}
Fe_2O_3{}_{\mathrm{(s)}} + SO_2{}_{\mathrm{(g)}} + SO_3{}_{\mathrm{(g)}}
\]

b. Decomposition by light:

Silver chloride decomposes in light to form silver and chlorine as,

\[
2AgCl{}_{\mathrm{(s)}}
\mathrel{\mathop{\longrightarrow}^{\mathrm{Light}}}
2Ag{}_{\mathrm{(s)}} + Cl_2{}_{\mathrm{(g)}}
\]

c. Decomposition by electricity:

Water decomposes in presence of electricity to form hydrogen and oxygen gases as,

\[
2H_2O
\mathrel{\mathop{\longrightarrow}^{\mathrm{Electricity}}}
2H_2 + O_2
\]