CBSE Class 10 Science- Ch-1 Chemical Reactions and Equations Notes

Science Chapter-1 Chemical Reactions and Equations
Science Chapter-1 Chemical Reactions and Equations

CBSE Class 10 Science Chapter 1 (Chemical Reactions and Equations) Notes

Hello Students, here we are uploading the important and short revision notes of CBSE Class 10 Science Ch-1 i.e. Chemical Reactions and Equations. While preparing notes you should always include important key points from NCERT text book of Science. These are the short notes and useful for the revision at the time of exams. We have taken these notes from various important and reliable resources like kvs and student support material and notes prepared by our students. So you can trust upon these notes for preparing your exams.


The process in which new substances with new properties are formed from one or more substances is called Chemical Reaction.  The substances which take part in chemical reaction are called Reactants.  The substances which are formed in a chemical reaction are called Products.

Download Notes of Ch-6 Life Processes

Examples :

(i) Digestion of food

(ii) Respiration

(iii) Rusting of iron

(iv) Burning of Magnesium ribbon

(v) Formation of curd

Chemical reaction involves :

  • Change in state
  • Change in colour
  • Change in temperature
  • Evolution of gas


Chemical Equation

A chemical reaction can be represented by chemical equation. It involves uses of symbol of elements or chemical formula of reactant and product with mention of physical state.

The necessary conditions such as temperature, pressure or any catalyst should be written on arrow between reactant and products. e.g., Magnesium is burnt in air to form magnesium oxide. 2Mg +O2→2MgO

 Types of Chemical Reactions

S NO Types of reactions Examples
1 Combination reaction

A single product is formed from two or more reactants.


2Mg +O2→2MgO


2 Decomposition reaction

A single reactant breaks down to yield two or more products.

i) Thermal decomposition




2Pb(NO3)2  → 2PbO  + 4NO2  +O2

ii) Electrolysis      2H2O →2H2  +O2
 iii) Photo chemical reaction       2AgBr →2Ag  +Br2
3 Displacement reaction

One element is displaced by another element.


Zn + CuSO4→ ZnSO4 + Cu

4 Double displacement reaction

Exchange of ions between reactants.


AgNO3 +NaCl →AgCl  +NaNO3

5 Redox reaction

Both oxidation and reduction take place simultaneously


CuO  + H2 → Cu + H2O



  1. 4. i)Exothermic reaction:A chemical reaction in which heat energy is evolved.

C + O2 →CO2 (g) + heat

ii)Endothermic reaction:A chemical reaction in which heat energy is absorbed.

ZnCO3 + Heat →ZnO + CO2

5 .Redox reaction:Chemical reaction in which both oxidation and reduction take place simultaneously.

Oxidation:Reaction that involves the gain of oxygen or loss of hydrogen.

Reduction:Reaction that shows the loss of oxygen or gain of hydrogen

ZnO + C Zn + CO

ZnO is reduced to Zn -reduction

C is oxidized to CO ——oxidation

Effects of oxidation reactions in our daily life:

   a)  Corrosion: It is an undesirable change that occurs in metals, when they are attacked by moisture, air, acids and bases.

Corrosion (rusting) of iron: Fe2O3. xH2O (Hydrated iron oxide)

Corrosion of copper:CuCO3.Cu (OH) 2 (Basic copper carbonate)

Corrosion of silver:Ag2S (Silver sulphide)

Corrosion of Aluminum: Al2O3 (Aluminum oxide)

b) Rancidity: Undesirable change that takes place in oil containing food items due to the oxidation of fatty acids.

Preventive methods

        (1)Adding antioxidants to the food materials.

(2) Storing food in air tight container

(3) Flushing out air with nitrogen gas.

(4) Refrigeration


CBSE Science Class 10 Ch. 1 Important Questions with Answers (only hints)


Very short answer questions. (1 mark)

  1. Identify in the following reaction:

  2PbO +C→2Pb +CO

  1. the substance oxidised and
  2. the substance reduced.
  3. A shiny brown coloured element “x” on heating in air becomes black in

colour . Name the element “x” and the black coloured compound formed.

Ans:    Element ‘x’is Copper and the black coloured compound is cupric oxide Cu2O

Short answer type questions  (2 mark)

  1. Classify the following reaction as combination,decomposition,displacement and double displacement reaction:-

a)BaCl2 +H2SO4 → BaSO4 +2HCl

Ans: Double displacement reaction.

  1. b) 3CuSO4+ 2Al→ Al2 (SO4)3 +3Cu

1. c)ZnCO3 →ZnO +CO2

Ans: Decomposition reaction

  1. d) C +O2→CO2

Q.2. What is a precipitation reaction? Give an example.

Ans. Reaction in which an insoluble substance or precipitate is formed Na2 + BaCl2————BaSO4+2NaCl

Short answer type questions (3 mark)

  1. Give an example, each for thermal decomposition and photochemical decomposition reactions. Write balanced equation for the same.

Ans.Thermal decomposition – Heating of lime stone.                                                                      CaCO3→CaO +CO2

Photochemical decomposition – Action of light on silver bromide.

2 AgBr→2Ag +Br2


Jonali visited her grandmother during summer holidays.Her grandmother prepared chips for her and stored it in airtight containers.

  1. a) What value is shown by her grandmother?
  2. b) Why did Jonali’s grandmother store the snack in airtight container?

Ans: a) Scientific temperament / concern for health

  1. b) Toprevent the food items from rancidity.

Very long answer type questions (5 mark)

  1. (i) Write chemical equations for the following and balance them.
  2. a) Zinc carbonate(s) →Zinc oxide+ Carbon dioxide

Ans)  ZnCO3 →ZnO  +CO2

  1. b) Potassium bromide(aq) + Barium iodide(aq)→ Potassium iodide + Barium bromide.

Ans) 2KBr   +   BaI2  →  2KI   +  BaBr2

  1. Nitrogen + Hydrogen → Ammonia

Ans)  N+  3H2  →  2NH3

  1. ii) What happens when electricity is passed through acidified water ?

Decomposition of water takes place resulting in the formation of hydrogen and oxygen.


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