Class 10 Science notes – Chapter 1 -Chemical reactions

Class 10 Science notes are so useful for upcoming CBSE exams for better preparation and concept learning. Chapter 1 is about the basic knowledge of chemical reactions and equations. You will learn the concept of the balancing the equations. Also the types of reactions.

These notes will give you the full chapter learning of Class 10 Science chapter 1.

Class 10 Science notes


Chemical reaction and equations notes

Chemical reactions are the process in which new substance properties are formed.

During a chemical reaction, atoms of one element do not change into those of another element; only a rearrangement of atoms takes place in a chemical reaction.

  • The substances which take part in a chemical reaction are called reactants.
  • The new substances produced as a result of chemical reactions are

called products.


Magnesium +oxygen→(heat)→magnesium oxide

(As ribbon)   (From air)                (White powder)

More examples-

Souring of milk, formation of curd from milk, cooking of food,

process of respiration, rusting of iron, etc.

Characteristics of chemical reactions:

The easily observable feature which take place as a result of Chemical Reaction

are known as characteristics of Chemical→ Reaction

  • Important characteristics are:-
  1.     Change in state
  2.     Change in colour
  3.     Evolution of a gas
  4.     Change in temperature
  5.     Formation of precipitation

Chemical equation

The method of representing a chemical reaction with the help of symbols and

formulae of the substance involved in it is known as a chemical reaction.

Zinc  + sulphuric acid →  Zinc sulphate  + hydrogen

Symbol of zinc→Zn

Formula of sulphuric acid →H₂SO₄

Formula of Zinc sulphate is →ZnSO₄

Formula of Hydrogen is →H₂

Zn +  H₂SO₄ →  ZnSO₄ +  H₂

(reactant)             (product)

  • The substances which combine or react are known as reactants. Zinc and sulphuric acid are the reactants here.
  • The substances produced in a reaction are known as products. Zinc sulphate and hydrogen are products.
  • an arrow sign (→) pointing towards the right hand side is put between the reactants and products.

Balancing of chemical equation –

The process of making different types of atoms equal on both sides of an equation

is called balancing of equations.

For example –

Hydrogen burns in oxygen to form water.

This reaction can be written in an equation


Reactants          products

No.of H atom-        2                         2

No.of O atom-        2                          1

We have to balance ‘O’. we will multiply H₂O by 2 so that


Reactants          products

No of H atom           2                       4

No of O atom           2                       2

Now hydrogen (H) becomes unbalanced so we will multiply by 2 in H₂


Reactants          products

No of h atom            4                       4

No of o atom            2                        2

*Balanced chemical equation:

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products .

 Zn+ H₂SO₄→ ZnSO₄+ H₂ 

  Reactants         products 

No of Zn atom:           1                        1

No of H atom:            2                          2

No of S atom:             1                         1

No of O atom:             4                        4

So there is an equal number of atoms of different elements in the reactants and

products, so the above equation is a balanced equation.

*so a balanced chemical equation has equal masses of various elements in  reactants

and products.



                          Reactant           products

No of H atom           2                      4

No of O atom           2                       2

Here no of elements of oxygen is unequal so this equation is called unbalanced chemical equation .

More example-

  1. Fe+H₂O→ Fe₃O₄ +H₂

                                   Reactant           products

No of fe atom          1                    3

H atom           2                   2

O atom           1                   4


                                       Reactant        product

O atoms           4                4

H atoms           8                2


                                     Reactant       products

Fe atoms                  3                3

O atoms                    4                4

H atoms                    8                8

  1. HNO₃+Ca(OH₂) →Ca(NO₃) ₂+H₂O
  2. NaOH+H₂SO→Na₂SO₄+H₂O
  3. NaCL+AgNO₃→AgCL +NaNO₃
  4. BaCL₂+H₂SO→BaSO₄+HCl


2) 2HNO₃+Ca(OH₂) →Ca(NO₃) ₂+2H₂O

3) 2NaOH+H₂SO→Na₂SO₄+2H₂O



Writing symbols of physical states

The gaseous , liquid, aqueous and solid states of reactants and products are

represented by the (g)(l)(aq)and (s) respectively


CO(g)+ 2H₂(g) CH₃OH(l)

340 atm


6CO₂(aq)+12H₂O(l)→C₆H₁₂O₆ (aq)+6O(aq)+6HO(l)


Photosynthesis reaction-

6CO₂(aq)+12H₂O(l)→C₆H₁₂O₆ (aq)+6O(aq)+6HO(l)

Types of chemical reaction-

1)combination reaction-

A reaction in which a single products is formed from two or more reactant is known as a combination reaction

CaO(s) + H2O(l) → Ca(OH)2

Slaked lime is used for white washing walls calcium hydroxide reacts slowly

with the carbon dioxide in air to form a thin layer of calcium carbonate.


Ca(OH)2 (aq)    +    CO2 →  CaCO3 (s) +  H2O (l)

(calcium hydroxide)             (calcium carbonate)

2)burning of coal-

C(s)+O₂ (g) →CO₂ (g)

3) formation of water from H₂(g) and O₂(g)-

2H₂(g)+O₂(g) →2H₂O(l)+heat

When a large amount of heat is evolved .

This makes the reaction mixture warm . A reaction in which heat is released

along with the formation of products is called an exothermic chemical reaction.

Natural gas →CH4

Other examples of exothermic reaction are :

(i)burning of natural gas

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g) + Heat


  • (ii)The carbohydrates which we eat are broken down to form glucose.

This glucose combines with oxygen in the cell of our body and provides energy.The name of this reaction is respiration.

(iii)decomposition of vegetable matter is also an exothermic reaction.

2) decomposition reaction:


A reaction in which a single reactant breaks down to give simpler products.

This is a decomposition reaction


2FeSO4                →        Fe2O3 (s) + SO2 (g) + SO3 (g)

(ferrous sulphate)           (ferric oxide)


CaCO3(s)            →       CaO(s)  +CO2 (g)

(limestone)                     (quick lime)


Pb(NO3)2             →        2PbO (s)   +    4NO2 (g)   +      O2 (g)

(lead nitrate)                (lead oxide)   (nitrogen dioxide)   (oxygen)

A reaction which requires energy either in the form of heat, light.

Or electricity for breaking down the reactants.

Such reactions in which energy is absorbed are known as endothermic                   reactions


2AgCl (s)              →        2Ag(s) + Cl2 (g)

(ferrous sulphate)           (ferric oxide)

3)displacement reaction

A reaction in which a substance displaced or removed another element.      This  The reaction is known as displacement reaction

Fe(s)  + CuSO4 (aq)  →  FeSO4 (aq) + Cu (s)

(copper sulphate)             (iron sulphate)

Zn(s)  + CuSO4 (aq)  →  ZnSO4 (aq) + Cu (s)

(copper sulphate)             (zinc sulphate)

4)double displacement reaction-

Na2SO4 (aq) + BaCl2 (aq) →  BaSO4 (s) + 2NaCl (aq)

PbNO2 + KI →  PbI2 + KNO2

5)oxidation and reduction-

If a substance gains oxygen during a reaction it is said to be oxidized.

If a substance loses oxygen during a reaction it is said to be reduced.


2Cu + O2            →       2CuO


CuO + H2     →       Cu + H2O

A reaction ,in which one reactant is oxidized while other gets reduced during

a reaction, such  reactions are called oxidation-reduction or redox reactions.


CuO + H2     →       H2O  +  Cu


ZnO + C → Zn + CO

MnO2 + 4HCl → MnCl2 + 2H2O + Cl2


When a metal is attacked by substances around it such as moisture ,acid etc. it is said to corrode and this process is corrosion.

The black coating on silver and green coating on copper are examples of corrosion.


Spoilage of food in such a way that it becomes undesirable

(and usually unsafe) for consumption.

  • *When fats and oils are oxides, they become rancid and their smell and

taste changes.

  • *Usually substances which prevent oxidation (antioxidation )are added to food containing fats and oils.


(1)why cannot a chemical change be normally reversed?

(2)why should a magnesium ribbon be cleaned before burning in air?

(3)why do we apply points on iron articles?

(4)oils and fats containing food items are flushed with nitrogen why?

(5)what happens chemically when quick lime is added to water?

(6)why respiration is considered an exothermic reaction?

(7)with the help of an activity show that iron is more reactive than copper?

(8)why does the colour of copper sulphate solution change when an iron nail is

dipped in it?

(9)What is an exothermic and endothermic reaction ?Give examples.

So we hope, You got the accurate notes for the class 10 science preparations. Also check notes of the chapters of the class 10 science ncert book. 

Class 10 ncert chapter notes

Class 10 Science quizzes


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