Class 6 Science Chapter 6 Changes Around Us, Reversible Change, Irreversible Change (For CBSE, ICSE, IAS, NET, NRA 2022)

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Changes Around Us


  • Everything around us in the environment undergoes a change after a certain period.
  • Some changes are temporary while some are permanent.
  • New leaves come out with the old ones turning yellow and falling down the trees.

Two Types of Changes

Reversible Change

  • Changes that can be reversed are known as reversible changes.
  • Actions may be reversed or the conditions may get changed.
  • Some of the examples are freezing of water, melting of ice, folding of paper, etc.

Irreversible Change

  • Those changes that cannot be reversed are known as irreversible changes.
  • Some of the examples are rusting of iron, cooking, burning of paper, etc.

Two Major Types of Changes That Substances Undergo

Physical Change

  • There is no change in the composition of the matter.
  • No new substance is formed after the change.
  • These changes are usually reversible.
  • Some of the examples are Freezing water to make ice cubes, Boiling water evaporating, Hot shower water turning to steam, melting of wax, Breaking Glass, Chopping wood, etc.

Chemical Change

  • New substance is formed after the change.
  • These changes are often reversible.
  • These changes cannot be reversed by simple physical means.
  • These changes have a direct impact on the chemical bonds and molecular composition of the material.
  • Some of the examples are rusting of iron, electroplating, metabolism, Chemical Battery, Fireworks, etc.
Electroplating Process

Causes of Change


  • Certain things may undergo change due to force.
  • Some of the examples are movement of vehicles, the balloon gets in flattened on blowing air into it, hammering a piece of gold, and making designs out of it, etc.


  • On application of thermal energy to a substance its temperature increases which changes its state from solid to liquid (melting) , liquid to gas (vaporization) , or solid to gas (sublimation) .
  • One of the examples is that of an ice which melts and turns into water.

Ways to Bring About Changes in Substances

Mixing Two Substances Together

  • One of the examples is that of adding a small amount of curd to the warm milk.
  • This converts warm milk into curd which is an irreversible change.

Expansion and Contraction

One of the examples is that of the jammed metal lid of a jam jar that can be opened by heating.

Other Changes

Based on Speed

Fast Changes

For example, switching off the fan.

Slow Changes

For example, growth of a child into an adult.

Based on Energy

  • Heat gets absorbed in the process i.e.. , Endothermic.
    • For e. g. , Condensation of water.
  • Heat energy is given out in the process i.e.. , Exothermic.
    • For e. g. , Photosynthesis.

Based on Time Interval

Periodic Changes

  • For example, change in phases of moon.
  • These changes occur repeatedly after regular intervals of time.

Non-Periodic Changes

  • For example, natural disasters.
  • These changes that don՚t repeat themselves at regular intervals of time.

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