Page 2 - Lesson Notes

 Let us take an example of Water Cycle as a reversible change.

 When the water body is heated by the sun rays, it changes to steam, i.e., Evaporation.

 The vapourised steam is then condensed to form the clouds, i.e., Condensation.
 The water is then released from clouds back to the land surface or water bodies, in the

form of rain, freezing rain, sleet, snow, or hail, i.e., Precipitation.

 Thus, water cycles involves a series of repetitive reversible changes forming a cycle.

IRREVERSIBLE CHANGE:

 A change which cannot be reversed to form the original substance is called an
irreversible change.

 Irreversible changes are permanent changes and cannot be undone.
 An irreversible change may also results in the formation of a new substance.

 E.g., growth of living things, cooking of food, digestion of food, burning of coal or

paper, ripening of fruits, curding of milk, raw egg to egg omblete, etc.
 Mixing and Heating usually brings about irreversible changes

2