Physical and Chemical Changes Class 7 Science Notes - Chapter 6

In our day to day life, we come across many changes such as rusting of iron, liting of a match, bread becoming toast, etc. All these changes are either a chemical change or a physical change.

Changes can be classified into two types viz physical change and chemical change.

  • Physical change is a change in which the molecular arrangements are rearranged and the chemical composition remains as it is. It is usually a reversible process. During a physical change, there is no formation of the new product. Physical properties such as size, color, shape, of the substances changes. Example, freezing of water.
  • A chemical change is a change in which the chemical composition of a substance is changed to transform into a new substance. It is usually an irreversible process. Whenever a chemical change occurs it forms a new product. Example, the setting of curd.

You can distinguish between the two as follows:

Physical Change Chemical Change
Reversible Irreversible
No new products formed New products formed

Few Important Questions

  1. Explain if photosynthesis is a chemical or physical change.
  2. Give two examples for each-
    1. Physical change
    2. Chemical change
  1. Answer true or false-

Formation of manure from leaves is a chemical change.

Condensation of steam is a physical change.

  1. Fill in the blanks –

Baking soda is chemically known as ___________

A change in which new substance is formed is called ___________ change

  1. Explain the setting of curd as a chemical change.
  2. How can we prevent rusting of iron? Explain in detail.
  3. Distinguish between physical and chemical change.
  4. Name two methods by which we can prevent the rusting of iron.

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Which is the correct equation for aerobic respiration in humans?