Section outline

    • Physical properties of a substance are: shape, size, colour & state.

      Definition of physical change:

      A change in which a substance undergoes change in the physical properties is called as a physical change. 

      Properties of physical change:

      1. It effects only the physical properties of a substance.
      2. It does not change the chemical composition of the substance.
      3. Physical changes are mostly reversible (means the original substance can be obtained again).
      4. No new substance is formed.
    • Examples:

      Some of the most common examples of physical changes in our daily life:

      1. Melting: 
      • When ice is heated, it melts into water.
      • This is a physical change as the chemical composition of water remains the same (H2O).
      • Also, when we freeze water, we can obtain ice again.
      2. Dissolving:
      • When salt is dissolved in water, it forms a saltwater solution.
      • The salt can be obtained again by evaporating the water.
      • Similarly, we can dissolve sugar and form solution, then obtain it back by heating the solution.
      3. Shaping clay:
      • Clay can be given any shape.
      • It can be changed back to its original form.
      4. Mixing of sand and water:
      • A mixture of sand and water can be separated again by process of sieving or sedimentation.
      5. Change of state of a substance.

    • Physical Irreversible changes

      There are some physical changes that are irreversible.

      Examples:

      1. Shredding of paper:
      • Cutting of paper is a physical change.
      • But you cannot obtain the original shape of paper again from the pieces.
      2.Grinding or breaking of rock.
      3. Breaking of glass:
      • Glass is broken into pieces it cannot be restored back to its original shape.

      Tough these changes are irreversible, they are physical because:

      • There is only change in the physical properties.
      • No change in chemical composition of new substance.
      • But the original shape or size of the original substance cannot be restored back.

      Thus, these changes are physical irreversible changes.

    • Experiments to observe physical changes:
      1. Melting Ice: Place ice cubes in a bowl and observe how they melt into water when left at room temperature.
      2. Again freeze this water and see you get the ice cubes back!
      3. Dissolving Sugar: Add sugar to a glass of water and stir. Observe how the sugar disappears, demonstrating a physical change.
      4. Any change of state experiment.
      To Remember:
      • Physical Change: change in just the physical properties & no new substance is formed.
      • It can be reversible or irreversible.