Question

Give two examples of reversible and irreversible changes.

Answer 1

Hint: A change can be of two types i.e., physical change and chemical change. The changes which occur in the physical properties of a substance such as shape, size and nature is referred to as a physical change while a change in which chemical properties of a substance changes is known as chemical change.

Complete answer:
Reversible change: Any changes which can be reversed or follow temporary conversions are known as reversible changes. Processes like melting, boiling, evaporation are considered as reversible changes. Thus, most of the reversible changes are considered as physical changes.
Examples:
1. Melting of ice: When the ice is melted, the solid phase of water molecules changes into its liquid phase but the properties remain the same and it is possible to convert the liquid back to ice by freezing. So, it is a reversible change.
2. Moulding clay: when a piece of clay is moulded, the shape of clay changes but no new substance is formed. So, this physical change is considered as a reversible change.
Irreversible changes: These changes are permanent and cannot be reversed. The reactants in the irreversible change react to form an entirely new compound which does not have any tendency to reach back to its original state. Thus, all chemical changes are considered as irreversible changes.
Examples:
1. Rusting of iron: iron reacts with moist oxygen to form iron oxide which is known as rusting and it is a chemical change as it is impossible to extract iron from rust.
2. Burning a piece of wood is also considered as a chemical change because on burning, it converts into ash and smoke. Ash has different properties as compared to wood so, it is impossible to convert it back to wood.

Note:
It is important to note that all chemical changes are irreversible changes but all physical changes are not reversible changes. A physical change may be reversible or irreversible. For example, change in height of a person is a physical change and it is an irreversible change.