Class 10 Science

Chemical Reaction

These notes are based on the chapter Chemical Reactions and Equations from NCERT book based on CBSE syllabus.

Everyday examples of chemical reaction

Milk is left at room temperature during summers.

Change: Milk gets curdled most of the time.

An iron girdle/pan/nail is left exposed to humid atmosphere.

Change: A brownish layer forms on iron girdle or pan or nail.

Grapes get fermented.

Change: Grapes develop a strange taste.

Food is cooked.

Change: Food becomes tastier and is easier to digest.

Food gets digested in our body.

Change: Food changes into simple nutrients.

We respire.

Change: Food is oxidized to produce energy for the body.

What is common in all these changes is that a new substance is formed after the change. You have read in earlier classes that when a new substance is formed after a change, the change is called a chemical change. Chemical Reaction is another name for chemical change.

Activity: Burning the magnesium ribbon in air

Let us do an activity to understand chemical reaction or chemical change.

Things You Need

A magnesium ribbon, pair of tongs, Bunsen burner, watch glass

Mganesium Ribbon Experiment Setup




We can say that a chemical reaction involves all or any of the above changes. There can be a change in colour, change in state, change in temperature, etc. In all cases of chemical reaction, a new substance is formed.

Signs of Chemical Reaction

  1. Change of state of substance
  2. Change of colour of substance
  3. Evolution of heat
  4. Absorption of heat
  5. Evolution of gas
  6. Evolution of light
  7. Evolution of sound, etc.

It is important to remember that a new substance is always formed at the end of a chemical reaction. Out of the list of various signs of chemical reaction, only some of the signs can be seen in a given chemical reaction. There can be change in state of substance in one chemical reaction, and there can be change of colour in another chemical reaction. Heat may be absorbed in one chemical reaction, and heat may be released in another chemical reaction.