Rusting occurs due to the exchange of electrons between the two elements : oxygen and iron. Exchange of electrons between elements is an electrochemical reaction.
A redox reaction is a type of electrochemical reaction where oxidation and reduction occur simultaneously. Redox is the short form for “reduction and oxidation”.
According to it oxidation is defined as ‘addition of oxygen or an electronegative element to a substance (or) removal of hydrogen (or) an electropositive element from a substance’.
Reduction is the opposite of oxidation. Reduction can be defined as‘removal of oxygen (or) an electronegative element from a substance or addition of hydrogen (or) an electropositive element to a substance’.
Thus according to the classical concept, redox reactions can be defined as” the reactions in which both oxidation and reduction takes place simultaneously”.
Reduction + Oxidation = Redox
i. When Mmethane reacts with Oxygen to give Carbon dioxide and water. During this reaction Carbon is oxidised due to removal of Hydrogen and simultaneously Oxygen is reduced due to addition of Hydrogen.
ii. In the reaction Copper oxide with Copper sulphate gives copper and Sulphur dioxide.
During this reaction oxygen an electronegative element is removed from Copper oxide and Copper an electropositive element is removed from Copper sulphate.
Examples of reduction reactions:
+ Heat → 2Hg(l)
Removal of oxygen from a substance
Removal of an electronegative element from a substance
Addition of hydrogen to a substance
Addition of an electropositive element to a substance