Work done by a van der waal gas/real gas in a expansion

[Zachary96]

Edited: To summarize the below attached jpg file is the formula for work done by a van der waals gas in a isothermal reversible expansion.

Is there a way to find the work done by a van der waal gas in a isothermal irreversible expansion? i.e the real gas expands against a constant pressure (in a balloon)

 

[Chestermiller]

Sure. But you may not be able to get an analytic expression. You drop the pressure from p_i to p_f at time zero, and then you hold the pressure at p_f until the system equilibrates at the new state. It this the process you are envisioning?