Redox reactions are classified into the following types:
(1) Combination reactions: When two or more substances combine to form a single substance, the reactions are called combination reactions.
Example: 2Mg + O2 → 2MgO
(2) Decomposition reactions: Chemical reactions in which a compound splits up into two or more simpler substances are called decomposition reaction.
Example: 2KClO3 → 2KCl + 3O2
(3) Displacement reactions: The reactions in which one ion or atom in a compound is replaced by an ion or atom of the other element are called displacement reactions.
Example: CuSO4 + Zn → ZnSO4 + Cu
(4) Disproportionation reactions: The reactions in which an element undergoes simultaneously both oxidation and reduction are called as disproportionation reactions.
Example: 2HCHO + H2O → CH3OH + HCOOH
(5) Competitive Electron transfer reactions: These are the reactions in which redox reactions take place in different vessels and it is an indirect redox reaction. There is a competition for the release of electrons among different metals.
Example: Zn(s) + Cu2+ → Zn2+(aq) + Cu(s)
Here Zn – oxidised; Cu2+ reduced