Question

Give examples to explain the difference between changes that can or cannot be reversed.

Answer 1

Chemical Change

• The change in which the molecular composition is altered and a new product is formed is called a chemical change.
• Chemical changes create a new product.
• The changes in Chemical change are irreversible and permanent.
• Example: Burning of wood

Physical change

• In physical change, the arrangement of molecules is altered leading to change in state.
• No new products are formed, and the molecular composition remains totally the same.
• Example, the molecular composition of ice and water is not altered, during melting of ice.

Difference between changes that can or cannot be reversed

Reversible changes	Irreversible changes
Reversible changes are those in which system can be returned to its original state by following a reversible path ..	Irreversible changes are those in which system cannot return to its original state.
2. Example: Melting of ice	2. Example: Burning of a piece of paper.
3. Ice gains heat and starts melting to form water, these water can be turned into ice by lowering the temperature (keeping it in the freezer), therefore, it is a reversible change.	3. When a piece of paper is burnt, it turns into ash, releasing carbon dioxide and water vapour. These ashes cannot be turned back into paper, therefore, it is a irreversible change.