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CBSE Class 10 Chemistry Revision Notes for Chemical Reactions and Equations

Find out how to create a balanced chemical equation and learn about chemical reactions with CBSE Class 10 Chemistry learning resources. On TopperLearning, our experts support you to understand chemistry with CBSE Class 10 Chemistry notes such as CBSE Class 10 Chemistry notes, MCQs and NCERT solutions as per the latest syllabus.

Discover the nomenclature of organic compounds, properties of hydrocarbons and a lot more through our CBSE Class 10 Chemistry Carbon and its compounds worksheets. Learn to identify elements based on their properties using our CBSE Class 10 Chemistry Periodic Classification of Elements notes.

For practicing questions and answers, you can check out our CBSE Class 10 Chemistry Chapter-1 solutions for NCERT textbook questions. Similarly, you can move ahead by practicing CBSE Class 10 Chemistry Chapter-2 questions or reviewing CBSE Class 10 Chemistry Chapter-2 notes.

In the CBSE Class 10 Science Syllabus 2019-2020, you will find 25 marks allocated to Chemical Substances – Nature and Behaviour in Unit-I. You can easily score those marks by practicing questions from our CBSE Class 10 Chemistry sample papers with answers.

Learning the fundamentals of Chemistry in CBSE Class 10 is now easy. TopperLearning presents study materials for CBSE Class 10 Chemistry which will help you to achieve a good score in your examination. Here, we believe in making students understand the basic principles and terminology. So, we have created highly interactive videos wherein all the concepts are explained in detail. Our study materials consist of video lessons, revision notes, question banks, sample papers and past year question papers which give you deeper insight on topics in Chemistry.

All our study materials are created by subject experts who have experience in teaching. Chemistry is an important subject and is a crucial subject in Science, so learning the fundamentals is important. While creating the study materials, we personally take care that they are in accordance with the latest CBSE syllabus and revised according to the changes prescribed. Apart from our study materials, students can also learn from our NCERT and RD Sharma textbook solutions which are available free of cost. Our comprehensive set of study materials acts as a perfect guide when doing homework and preparing for the examination.

Chemical Equation

Writing Chemical Equations

  • In a chemical reaction, the reactants are written on the left hand side and the products on the right hand side of the equation.
  • An arrow (→) pointing towards the products is inserted between the reactants and the products. It also represents the direction of the reaction.
  • A single arrow (→) indicates the direction in which the reaction proceeds.
  • A double arrow ( ⇋ ) indicates a reversible reaction, i.e. the products recombine to form the reactants
  • A plus sign (+) is inserted between two or more reactants or products formed.
  • If reactions are carried out under specific conditions of temperature, pressure, catalyst etc., then these conditions are mentioned on the arrow.
  • The chemical equation can be made more informative by mentioning the physical states of the reactants and products.
  • If gas is liberated as a product then it is represented by an arrow pointing upwards (↑). If the product formed is in the form of a precipitate, it is represented by an arrow pointing downwards (↓).

Balancing the Chemical Equations

  • In a balanced chemical equation, the total number of atoms of each element of the reactants on the left hand side of the equation is equal to the number of atoms of the products formed on the right hand side of the equation.
  • The total mass of the reactants is equal to the total mass of the products or the number of atoms of each element before the reaction and after the reaction is equal.

Steps Involved in Balancing a Chemical Equation
Consider the chemical reaction between magnesium and oxygen to understand the steps involved in balancing a chemical equation.

Step 1
Let us first write the word equation for this reaction.
Magnesium + Oxygen → Magnesium oxide

Step 2
Write the chemical equation for the reaction between magnesium and oxygen.

Mg + O2 → MgO

Step 3
Count the number atoms of an element occurring on both L.H.S. and R.H.S. in this equation.
Mg + O2 → MgO

Component Reactant Product
Magnesium 1 1
Oxygen 2 1

This is an unbalanced equation.

Step 4

  • To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.

            begin mathsize 12px style box enclose Mg space space space plus space space space box enclose straight O subscript 2 end enclose space space space space space space space rightwards arrow with blank on top space space space space space box enclose MgO end style

  • Choose a reactant or a product which has the maximum number of atoms in it. In that compound, select the element which has the maximum number of atoms. In this equation we shall select MgO i.e. magnesium oxide and the element oxygen in it.
  • To balance the oxygen atoms, let us multiply magnesium oxide molecule by 2 on the right hand side. The equation can now be expressed as,

            Error converting from MathML to accessible text.   

Component Reactant Product  
Magnesium 1 1 x2 = 2
Oxygen 2 1 x2 = 2


Step 5

There are two oxygen atoms on either side of the equation but one magnesium atom on the reactant's side and two on the product's side. Therefore, multiply the magnesium atom by 2 on the left hand side.

Component Reactant  Product
Magnesium 1 x 2 = 2 2
Oxygen 2 2

Balanced equation is,

Error converting from MathML to accessible text.

∴ The number of atoms of each element of reactants = The number of atoms of each element of products

Step 6
Writing Specific Conditions on the Arrow
The reaction is carried out in the presence of ‘Heat’. On heating, magnesium combines with oxygen present in air to form magnesium oxide.

Error converting from MathML to accessible text.

Step 7
Writing Symbols of Physical States

begin mathsize 12px style 2 space Mg space left parenthesis straight s right parenthesis space space plus space space straight O subscript 2 left parenthesis straight g right parenthesis space space space space space rightwards arrow with Heat on top space space space 2 space MgO space left parenthesis straight g right parenthesis end style

Using these steps, you can balance any chemical equation.

Types of Chemical Reactions

Combination Reaction
When two or more substances combine to form a single product, the reaction is known as a combination reaction.
For example:
In the laboratory, iron sulphide is prepared by mixing iron and sulphur.

Fe(s) + S(s) →  FeS(s)

  • Endothermic Reaction: The reactions accompanied by the absorption of heat are called endothermic reactions.
  • Exothermic Reaction: The reactions accompanied by the evolution of heat are called endothermic reactions.

Decomposition Reaction
A chemical reaction in which a single compound splits into two or more simple substances is called a decomposition reaction.
For example:
When mercuric oxide is heated in a crucible, the orange-red powder begins to darken and a silver mirror begins to deposit on the cooler parts of the crucible.

2HgO(s)     size 12px space size 12px space size 12px rightwards arrow with size 12px Heat on top    2Hg(s)   +  O2
Mercuric oxide             Mercury    Oxygen

  • Thermal Decomposition Reaction: The decomposition reactions carried out by heating are known as thermal decomposition reactions.
  • Photochemical reaction: The chemical reactions which proceed with the absorption of light energy are called photochemical reactions.

Displacement Reaction
Reactions in which the more reactive element displaces the less reactive element from its compound are called displacement reactions.
For example:
Zinc displaces copper in copper sulphate to form zinc sulphate.
Zn(s)   +   CuSO4 (aq)     →     ZnSO4 (aq)  +  Cu(s)
Zinc      Copper sulphate        Zinc sulphate      Copper

Double Displacement Reaction
Reactions in which ions of the reactants exchange places to form two new compounds, are called double displacement reactions.
For example:
Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
NaOH(aq)  +  HCl(aq)  →  NaCl(aq)  +  H2O(l)

Oxidation Reactions
Reactions which involve the addition of oxygen or the removal of hydrogen are called oxidation reactions.
For example:
C(s) + 2H2 (g)  →  CH4 (g)

Reduction Reactions
Chemical reactions in which the reactants gain hydrogen are reduction reactions.
For example:
Fe2O3      +       3CO         s→       2Fe       +     3CO2
Ferric oxide    Carbon monoxide     Iron       Carbon dioxide

Redox Reaction
The chemical reaction in which oxidation and reduction takes place simultaneously is known as a redox reaction.

The slow process of decay and destruction of metals due to the action of air, moisture or acids is called corrosion.

For example:
Iron combines with oxygen present in the air, in the presence of water, to form a red-brown flaky substance called rust. This process is commonly called the rusting of iron.
The chemical formula of rust is Fe2O3. x H2O.

Prevention of Corrosion

  • Corrosion damages buildings, bridges, ships, automobiles and other articles made of iron. Hence, prevention of corrosion is necessary. This will not only save money but can also prevent the occurrence of accidents.
  • It can be prevented by processes like galvanising and electroplating with other metals.


  • Oils and fats react with oxygen and get oxidised or turn rancid. This process is called rancidity.
  • Rancidity can be prevented by keeping food in air tight containers or by using antioxidants.
  • Antioxidants are used to prevent oxidation of food containing fats and oils.
  • Storage of food in air tight containers also decelerates oxidation.

Chemistry Chapters for Revision Notes

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