Theory:

The change in chemical properties of a substance is known as chemical change. In this change, a new substance is formed, and these changes are irreversible in nature. Irreversible changes are permanent.
Example:
Burning of a candle, rusting of iron, burning of paper, burning of matchstick, cooking of vegetables, formation of curd from milk, digestion of food, heating sugar to form caramel, etc.
Bursting a balloon: If a balloon is blown and pricked with the pointed tip of a needle, it cannot regain its original form. This is an irreversible change.
 
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Bursted balloon
 
Burning of matchstick: When the matchstick is burned, it turns into ashes. The ashes have an entirely new chemical composition than that of the unburnt matchstick. This change in the chemical composition of the substance is known as chemical change.
 
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Burned matchstick
  
Pot making: A pot is made using a lump of clay. The shaped pot can be rolled again into a lump which is a reversible process. But when the same pot is baked in an oven, it cannot be shaped into a lump of clay again. So, this process becomes irreversible chemical change.
 
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Pot