Class 7
Chapter 6 Class 7 - Physical and Chemical Changes

A change in which one or more new substances are formed is a chemical change. 

  • It is a permanent change.  
  • It cannot be reversed .
  • It is often accompanied by:
    • Heat, light or any other radiation (for example - UV) being given off or absorbed.
    • Sound 
    • A change in smell / a new smell 
    • A colour change
    • Formation of a gas .

Hence, Digestion, Photosynthesis, and even simpler phenomena such as burning, spoiling of food, neutralisation, etc are all chemical changes.

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo