NCERT Class X Science Solutions: Chapter 1-Chemical Reactions and Equations Part 3

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Question 12:

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.


  1. Thermal decomposition:

  1. Decomposition by light:

  1. Decomposition by electricity:

Question 13:

What is the difference between displacement and double displacement reactions? Write equations for these reactions.


In a displacement reaction, a more reactive element replaces a less reactive element from a compound.

; Where A is more reactive than B

In a double displacement reaction, two atoms or a group of atoms switch places to form new compounds.

For example:

Displacement reaction:

Image result for displacement reaction

Displacement Reaction

Double displacement reaction:

Image result for double displacement reaction

Double Displacement Reaction

Question 14:

In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.


Question 15:

What do you mean by a precipitation reaction? Explain by giving examples.


A reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.

For example:

In this reaction, calcium carbonate is obtained as a precipitate. Hence, it is a precipitation reaction.

Another example of precipitation reaction is:

In this reaction, barium sulphate is obtained as a precipitate.

Question 16:

Explain the following in terms of gain or loss of oxygen with two examples each.

  1. Oxidation

  2. Reduction


  1. Oxidation is the gain of oxygen.

For example:

In equation (i), H2 is oxidized to and in equation (ii), Cu is oxidised to CuO.

  1. Reduction is the loss of oxygen.

For example:

In equation (i), is reduced to CO and in equation (ii), CuO is reduced to Cu.

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