1. The problem statement, all variables and given/known data Why does the Van der Waals equation adjust pressure up and volume down? 2. Relevant equations (P + a)(V-b) = nRT (overly simplified, but it gets the point across). 3. The attempt at a solution Okay. Volume refers to total free volume in a container in the context of the gas law. I can understand why volume is adjusted down relative to the ideal gas law equation (PV = nRT). Gases aren't point masses and actually occupy some volume. However, why is pressure adjusted up? Gas molecules may attract and participate in inelastic collisions. This would seem to decrease the actual pressure. Why then would pressure need to be adjusted up?