Van der Waal's equation

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Van der Waal's equation | 1st year chemistry unit 3
Van der Waal's equation | 1st year chemistry unit 3

Why the volume correction is done by van der Waal?

Ans. Actual volume of gas molecules is not negligible as compared to the total volume of vessel. Therefore, Van der Waal corrected the volume factor in general gas equation. So, excluded volume is subtracted from total volume of vessel to get the free volume available for gas molecules.

                                      Vfree = Vvessel – b (excluded volume)

Why the pressure correction is done by Van der Waal?

Ans. Forces of attraction present between molecules of real gas. Therefore, Van der Waal corrected the pressure correction in general gas equation. Lessened pressure is subtracted from ideal pressure to get the observed pressure.

                                      Pobs = Pideal – P’ (lessened pressure)

What is the physical significance of Van der Waal’s constants ‘a’ and ‘b’ ?

Ans. The factor ‘a’ is for attractive forces present between the molecules of the gas. If attraction forces are strong, greater will be factor ‘a’.

The factor ‘b’ is the excluded volume of gas. It is related to the volume which is occupied by the gas molecules and that volume which is not available to the gaseous molecules.

Derive the units of ‘a’ and ‘b’.

Van der Waal's equation | 1st year chemistry unit 3


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