Chemistry Class-11: Chapter –5. States of Matter Part – 5

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Question: 31

One of the assumptions of kinetic theory of gases is that there is no force of attraction between the molecules of a gas.

State and explain the evidence that shows that the assumption is not applicable for real gases.


Real gases can be liquefied on cooling and compressing proving that forces of attraction exist between the molecules.

Question: 32

Compressibility factor, Z, of a gas is given as

(i) What is the value of Z for an ideal gas?

(ii) For real gas what will be the effect on value of Z above Boyle’s temperature?


(i) for ideal gas

(ii) For a real gas above Boyle’s temperature.

Question: 33

The critical temperature and critical pressure of are and

respectively. Can be liquefied at and pressure?


cannot be liquefied at by applying a pressure of atm. This is because the temperature is greater than critical temperature of .

Question: 34

For real gases the relation between p, and is given by van der Waals equation:

where ‘a’ and ‘b’ are van der Waals constants, ‘’ is approximately equal to the total volume of the molecules of a gas. ‘a’ is the measure of magnitude of intermolecular attraction.

(i) Arrange the following gases in the increasing order of ‘b’. Give reason.

(ii) Arrange the following gases in the decreasing order of magnitude of ‘a’. Give reason.


(i) because size increases in the same order.

(ii) intermolecular attractions are the highest in and lowest in because intermolecular forces increase with number of electrons in a molecule.

Question: 35

The relation between pressure exerted by an ideal gas and observed pressure is given by the equation

If pressure is taken in , number of moles in mol and volume in ,

Calculate the unit of ‘a’.

What will be the unit of ‘a’ when pressure is in atmosphere and volume in ?


We write the known units in the above equation.

If two values with same units are added then the units of result are same as added units.

Similarly, when is in and volume in

Question: 36

Name two phenomena that can be explained on the basis of surface tension.


(i) Rise or fall of the liquid in a capillary - capillary action.

(ii) Spherical shape of small liquid drops.

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