Take a look at the different processes taking place around you:

  • Plants preparing food by the process of photosynthesis
  • Iron structures turning reddish brown with time due to corrosion (rusting)
  • Dirt in clothes getting removed on washing with soap and water
  • Cake batter rising and getting cooked on baking
  • Burning of wood at a campfire


All of these processes that we observe in our day to day lives are a result of Chemical Reactions.

Chemical Change-Teachoo-01.jpg

What are Chemical Reactions?

It is a process by which new substances with new properties are formed .

In a chemical reaction one or more substances combine to form new substances.



Hydrogen reacts with Oxygen to form Water

Hydrogen + Oxygen     →        Water

        (Reactants)                   (Product)

Note : When Hydrogen and Oxygen react, they form a new substance Water, hence it is a chemical reaction


Is chemical reaction a result of Physical change or chemical change?

Chemical Reaction results in the formation of new substances. 

Thus we can say, it occurs because of chemical changes

Chemical Change vs Physical Change-01.jpg




No new substance is formed.

New substances are formed.

These changes are reversible

These changes are normally irreversible


When ice melts into water, it is a physical change

It is because ice and water are chemically same (both are H 2 O)

We can convert ice to water and vice versa.

Hence it is a physical change


Burning is chemical change

When a paper is burnt, it turns into carbon

This change cannot be reversed to get back paper

Hence it is a chemical change


Based on the above explanation of physical and chemical changes, we can confirm that chemical reactions occur as a result of chemical changes , as;

  • New products are formed as a result of chemical reactions and
  • The reaction is usually not reversible under the same conditions


Note : If the products can react to produce the reactants, then the reaction will be considered reversible.

Do elements change because of chemical reaction ?

The simple answer is, No

Atom of one element does not change into another element


They only rearrange to form new substances



Magnesium + Oxygen → Magnesium Oxide


During this reaction, Magnesium Oxide is formed which contains only Magnesium and Oxygen element (and not any new element )

Note- Magnesium ribbon burns with a dazzling white flame and changes into white powder. The white powder formed is Magnesium Oxide.

Burning of MG-Teachoo-01.jpg

What are reactants and products?

The substances which undergo chemical change in a chemical reaction are called reactants .

The substances produced as a result of chemical reaction are called products



Magnesium + Oxygen → Magnesium Oxide

In this case Magnesium and Oxygen are called Reactants

Magnesium Oxide is a Product


Magnesium + Oxygen → Magnesium Oxide

           (Reactants)                 (Product)



How to find whether chemical change has taken place?

If a chemical change takes place, it usually leads to following:

  • Change in state
  • Change in color
  • Evolution of Gas (Gas being formed)
  • Change in Temperature
  • Formation of precipitate

Example- Change in color of substances and evolution of gas in a chemical reaction


When we heat green coloured Ferrous Sulphate crystals in a boiling tube,

We observe that the green colour of Ferrous Sulphate changes .

We can also observe smell on burning of sulphur

This is because  on heating,

Ferrous Sulphate breaks down into Ferric Oxide (solid) , Sulphur dioxide (gas) and Sulphur Trioxide(gas)


2FeSO 4 → Fe2O 3 ​+ SO 2 ​+ SO 3

                                                 (Reactant)           (Products)

Heating Ferrous Sulphate-Teachoo-01.jpg

Ferrous Sulphate crystals and Ferric Oxide - Teachoo.jpg

Example- Change in Temperature


Calcium Oxide (Quick Lime) reacts with Water to produce Calcium Hydroxide (Slaked Lime) and Heat

CaO + H 2 O → Ca(OH) 2

                                                         (Reactants)      (Product)

Calcium Oxide Reaction-Teachoo-01.jpg

Example- Formation of precipitate


When Sodium Sulphate solution is mixed with Barium Chloride solution

It forms Barium Sulphate precipitate and Sodium Chloride

(Insoluble solid is called precipitate)

Formation of Barium Sulphate-Teachoo-01.jpg

Note : This Barium Sulphate is formed because of the reaction of positively charged ions of Barium and negatively charged ions of sulphur

Intext Question - Page 6 Q1, 

NCERT Exercise -

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo