Class 7 Chemistry Physical and Chemical Changes Changes occurring in a chemical change

Changes occurring in a chemical change

Chemical changes occurring in our day to day life involves following changes.

  • Change in colour

During rusting the iron articles undergoes change in colour. We have also observed that silver gets tarnished when kept for a long time. The metallic silver reacts with hydrogen sulphide or sulphur present in air and gets tarnished.

  • Change in state

On heating liquid changes its state and converts to vapour due to reaction within the particles caused by heat.


  • Change in odour

Due to chemical reaction food gets spoiled and smells really bad.

Fig. Fresh apple (left) Spoiled Food (right)


  • Change in temperature

Lime when mixed with water undergoes certain change that rises its temperature and makes it evolve heat and give a clear solution. Such reactions are called exothermic reactions.


  •  Release of gas

During Aerobic cellular respiration in human body energy molecules combines with inhaled oxygen and releases energy needed by the cells. It also releases Carbon Dioxide gas and water. Here is the overall equation for aerobic cellular respiration:

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