Kinetic, kinetic theory of matter, kinetic theory of matter some example

Kinetic theory of matter– Anything which has a mass and occupies space is called matter. the smallest unit of matter which can exist independently and exhibit all the physical and chemical properties of matter is called molecule. the following are some of the postulates of kinetic theory of matter which would help us to understand the concepts in this post better.

  1. The kinetic energy of molecules is directly proportional to the absolute temperature.
  2. Molecules always attract each other. The force of attraction between like molecules is called cohesive force. The same force between unlike molecules is called adhesive force.

The cohesive force depends on the space between molecules called inter-molecular space. more the space, less is the cohesive force. In solids the cohesive force is very strong as the inter-molecular space  is very less. if a force is applied to a solid, it is displaced from one place to another, but the relative positions of its molecules do not change. hence, solids have rigidity, definite shape and volume.

when the inter-molecular force is decreased by either decreasing the pressure or increase the temperature, a solid converts to liquid and liquid to gas. as cohesive force is less in liquids, they do not have rigidity and definite shape. However the force is strong enough to maintain the number of molecules, per unit volume, same. Hence, liquids have definite volume.

For gases, the cohesive force is extremely negligible. Hence, gases do not have rigidity definite shape and volume.

It is clear that, molecules in liquids and gases have more freedom of movement. Hence their relative position changes continuously. this gives liquids and gases a unique ability to from one point to another, even when no external force is applied. This property called fluidity’ and thus liquids and gases together are called fluids.

kinetic theory of matter some example

Example 1

Conduction of heat is not possible through gases. Explain with respect to kinetic molecular theory 


Conduction of heat in matter takes place by the transmission of agitation of one molecule to the other, and hence, the molecules should be closely packed. but in gaseous state, the molecules are very far from each other. hence, the heat cannot be transmitted from one molecule to another molecule, and thus, there is no conduction of heat through gases.

Example 2

A given mass of a gas is present in a cylinder of volume 10 L which can also be filled in a cylinder of volume 1 L. Explain the above statement with suitable reason / s.


The force of attraction between the gas molecules is negligible. As a result, the intermolecular space between the molecules of the gas is very high. Moreover, the molecules have high kinetic energy. thus, the molecules are free to move in all directions, and hence, can fill the available space easily due to which gas can completely occupy a cylinder having volume of 10 L. As intermolecular spaces are large in gas, they can easily be compressed, and hence, the same mass of gas can also be stored in a cylinder with 1 – L volume.

What are the three assumptions of the kinetic theory of matter?

  1. Every form of matter is composed of small particles called molecules.
  2. The empty space (gaps) that exists in between the molecules is called intermolecular space. 
  3. Molecules exert attractive forces, called intermolecular forces of attraction, upon one another. These forces decrease with an increase an the distance between the molecules. The force of attraction between similar molecules is called cohesive force and that between dissimilar molecules is called adhesive force. 

kinetic theory of matter questions and answers

kinetic theory of matter 10 questions and answers
1.Gas molecules have higher intermolecular force of attraction due to larger intermolecular space.
Answer- false 
2.The arrangement of a substance depends upon
Answer- pressure 
3.In which of the following substance intermolecular force of attraction is the maximum?
Answer- iron bar 
4.According to the kinetic molecular theory, explain the following.

  • Density of a liquid is the highest.
  • Gases are highly compressible where’s solids in are incompressible.
  • Liquids and gases are fluide, whereas solid are rigid.
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