Reversible Reaction

Reversible Reaction refers to a chemical reaction in which the products can covert back into their original state. For example, the evaporation (vaporization) and condensation (liquefaction) of water are examples of reversible reactions. When water is heated the liquid water evaporates and turns into water vapor, but this vapor can condense back into liquid water. 

Secondary cells also fall under reversible reactions, as they can be repeatedly charged and discharged. This is the most distinctive feature of secondary cells compared to primary cells. 

Irreversible Reaction

Irreversible reaction refers to a chemical reaction in which the products, once reacted, can’t covert back into the original state. For instance, the burning of paper is irreversible reaction as the ash and gases cannot be turned back into the original piece of paper. The browning in apple also falls under irreversible reaction because apples cannot be turned back into the original color when the exposed surface of sliced apple turns brown due to oxidation.