Ideal Gas vs. Van Der Walls

[CollectiveRocker]

Why does the Van Der Walls equation give a less value for pressure than the Ideal Gas equation does?

[mathlete]

Try look over this:
http://en.wikipedia.org/wiki/Van_der_Waals_equation

[Clausius2]

The main point is a VDW model gas has electrostatic interactions between particles. Thus, the particles are not flowing as free as in an ideal model gas. Therefore the pressure is smaller than the pressure predicted by VDW.