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As studied in Chapter 5 (States of Matter) a gas has no bounding surface and thus has no definite volume or shape.

In this chapter, we examine and learn to use the laws governing the behavior of gases. These laws, combined with the other properties of gases, form the basis for the Kinetic molecular theory of gases.

6.1 Properties of Gaseous State

Following are the five properties of gases which can be measured experimentally.


Gases are easily compressible.

The molecules in a gas are very far apart due to very low intermolecular forces. By external pressure they can be brought closer, thereby compressing the gas.


Gases do not have definite volume.

Molecules move easily and occupy the entire volume of the container and take the shape of the container.


Gases exert pressure in all directions.

Molecules are always in a state of rapid zig zag motion, colliding with each other and with the walls of the container. Collisions account for pressure. As the same number of molecules strike a given surface in unit time, gases exert pressure uniformly in all directions.


Gases diffuse easily.

Molecules of other substances can fill a large space between gaseous molecules. This is nothing but diffusion.


Gases have low density.

Due to large space, the number of units of molecules per unit volume of gas is very low compared to solids or liquids.

Gas Laws :

The quantitative relationship between volume, pressure, temperature and the rate of diffusion for a given quantity of gas are termed as ’Gas Laws’.

These Laws are

*       Boyle’s law

*       Charles’ law

*       Pressure-temperature law

*       Avogadro’s law

*       Graham’s law of diffusion


6.1 The Gaseous States Properties
6.2 Boyle's Law
6.3 Charle's Law
6.4 Pressure - Temperature Law
6.5 Gay Lussac's Law
6.6 Avogadro's Law
6.7 Graham's Law of Diffusion
6.8 General Gas Equation

Chapter 7

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