[Verse] Start from the law you know by heart PV equals nRT Point particles, no interactions Ideal limit, clarity But at high pressure, low temperature Assumptions start to fail Finite size and weak attraction Shift the measured pressure scale [Chorus] Real gas, the picture changes Two parameters, wide-ranging Pressure corrected, volume too van der Waals gives a better view [Verse] Molecules attract each other Pull the pressure slightly low Add the a-term back to fix it A! over V-M squared tells you so [Chorus] Real gas, the picture changes Two parameters, wide-ranging Pressure corrected, volume too van der Waals gives a better view [Verse] Particles have finite volume So available space is less V minus nb is the free volume That correction you must express [Bridge] Both corrections act together Pressure, volume linked as one Real behavior from interaction Not just motion, more than none [Final Chorus] Real gas, the picture changes Two parameters, wide-ranging Pressure corrected, volume too van der Waals gives a better view [Outro] Low density, corrections vanish Ideal behavior shows