Class 9 Chemistry Is Matter Around Us Pure Physical and Chemical Changes

Physical and Chemical Changes

  • Changes in energy are always accompanied by a particular chemical or physical change.

Physical Changes

  1. The changes in which no new substance is formed are called physical changes.
  2. The molecular composition remains totally same.
  3. For example, the molecular composition of ice and water is not changed.
  4. The energy needed to bring a physical change is equal to the amount of energy required to reverse the change. There is no change in energy.
  5. The changes are reversible and temporary. The reaction gets reversed if the cause producing the change is removed. For example, water on freezing forms ice and ice on melting forms water.
  6. Examples of physical change
    1. Dissolution of sugar in water
    2. Melting of ice
    3. Freezing of water
    4. Boiling of water
    5. Melting of wax

Chemical Changes

  • The change in which the molecular composition is completely changed and a new product is formed is called a chemical change. A new product is formed.
  • The changes in Chemical change are irreversible and permanent. A chemical change cannot be reversed by changing or altering the experimental changes.
  • During a chemical change the energy changes occur. There is an energy difference in the breaking of old bonds in reactants and formation of new bonds in products.
  • Examples of Chemical Change
    • Burning of wood or paper
    • Burning of camphor
    • Souring of milk
    • Burning of candle
    • Digestion of food

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