[P + (n2a/V2)](V - nb) = nRT What is the P represent? Is the pressure of ideal gas or the pressure we can measure from the real gas? Consider now it is the pressure of ideal gas but how do we get the value of P from an experiment of real gas? What if it is the pressure of real gas then why do we need to put (n2a/V2)? one more thing, Pv=RT, P= pressure exerted by the ideal gas ? v= volume of the container / volume occupied by gas? Thank you.