A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

Change in shape/nature of an object can be of two types. They are reversible changes and irreversible changes.

a) The changes in which the object/matter can be brought back to its original state is known as reversible changes.

    e.g., melting of wax, stretching of a rubber band etc.

b) The changes in which the object/matter cannot be brought back to its original state is called irreversible changes.

    e.g., burning of wood, cooking of food etc.

A chemical change happens when water is added to POP. This leads to a change in its composition and makes it harder, which is a permanent chemical change. Thus, the change to the POP is irreversible.