EK says we don't need to memorize the van der waals equation, but you should understand what the equation means and how to apply it. Basically, they will not give you a calculation to perform, unless they give you the equation, but...u should know that Vreal > Videal and Preal < Pideal.
Quoting from EK, "Since molecules of a real gas DO have volume, their volume must be added to the ideal volume. Thus Vreal > Videal (where Videal is calculated from PV=nRT). Second, molecules in a real gas do exhibit forces on eachother and those forces are attractive when the molecules are far apart. Since the predominant intermolecular forces in a gas are attractive, gas molecules are pulled inward toward the center of the gas, and slow before colliding with the container walls. Having been slightly slowed, they strike the container wall with less force than predicted by the kinetic molecular theory. Thus a real gas exerts LESS PRESSURE than predicted by the ideal gas law. Preal < Pideal (where Pideal is calculated from PV = nRT).
So for the van der waals equation, [P + a(n/V)^2](V -nb) = nRT, a and b are constants for specific gases. b is a measure of the actual volume occupied by one mole of gas. a reflects the strength of intermolecular attraction (ie..pressure).
