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For real gases van der Waals equation is written as

\left( {\text{p} + \frac{{\text{an}^2}} {{\text{V}^2 }}} \right)\left( {\text{V} - \text{nb}} \right) = \text{n}\,\text{RT}

 Where 'a' and 'b' are van der Waals constants.

Two sets of gases are:

(I)    O2, CO2, H2 and He

(II)    CH4, O2 and H2

The gases given in set - I in increasing order of 'b' and gases given in set - II in decreasing order of 'a' are arranged below. Select the correct order from the following:

  • Option 1)

    (I) O2<He<H2<CO2 (II) H2>O2>CH4

  • Option 2)

    (I) H2<He<O2<CO2 (II) CH4>O2>H2

  • Option 3)

    (I) H2<O2<He<CO2 (II) O2>CH4>H2

  • Option 4)

    (I) He<H2<CO2<O2 (II) CH4>H2>O2

 

Answers (1)

best_answer

As we learnt in

Vander waal constants -

Vander waal constant ‘a’ is measure of intermolecular attraction of a gas

-

 

 

Vander waal Constant -

Vander Waal constant ‘b’ is measure of size of molecule

-

 

 

Van der Waals constants a & b

a is the measure of intermolecular attraction of gas , b is the measure of the size of the molecule. So, the increasing order of b is clearly.

H_{2}< H_{e}< O_{2}< CO_{2}

and the decreasing order of a is 

CH_{4}> O_{2}> H_{2}


Option 1)

(I) O2<He<H2<CO2 (II) H2>O2>CH4

Incorrect 

Option 2)

(I) H2<He<O2<CO2 (II) CH4>O2>H2

Correct

Option 3)

(I) H2<O2<He<CO2 (II) O2>CH4>H2

Incorrect 

Option 4)

(I) He<H2<CO2<O2 (II) CH4>H2>O2

Incorrect 

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