Question

Explain and illustrate the origin of a & b in the van der Waal gas equation

Answer 1

Vanderawaal's equation is

( P+ an2/V ) (V-nb)=RT

The constants a and b have positive values and are characteristic of the individual gas. The van der Waals equation of state approaches the ideal gas law PV=nRT as the values of these constants approach zero. The constant a provides a correction for the intermolecular forces. Constant b is a correction for finite molecular size and its value is the volume of one mole of the atoms or molecules.

a is a measure of the attraction of the molecules for each other (due to van der Waalsforces). Its just a change to the ideal gas equation with corrected pressure and volume. a and b were added as in practical situation, intermolecular forces and different molecular size existed.