What the work claims
Fluids are composed of discrete particles with finite volume and mutual attraction. Gas non-ideality arises from those properties. The gas and liquid phases are not fundamentally distinct but continuous manifestations of the same molecular system.
How it was done
Van der Waals derived the equation in 1873 as part of his doctoral thesis at the University of Leiden. He assumed molecules exist, have finite size, and attract each other. He modelled intermolecular forces as hard repulsion plus weak attraction at distance. He introduced molecular volume and molecular attraction as physical parameters. He attributed gas non-ideality to intermolecular interactions.
What holds up
It describes both liquid and gas states. It accurately predicted fluid behaviour around the critical point. It showed qualitative and quantitative agreement with experiments. It enabled quantitative estimation of molecular size and attraction strength from experimental data. It unified gas and liquid phases as continuous states of the same nature.
What does not
It does not quantitatively predict fluid behaviour across all temperatures, pressures, or substances. It does not describe molecular motion, kinetics, or quantum effects. It does not establish molecular existence as fact — only that assuming it yields predictive power.
Why it matters beyond the lab
It shifted thermodynamics from phenomenological description to molecular explanation. It gave experimentalists a way to estimate molecular size and interaction strength decades before direct observation. It made molecular reality plausible to sceptics — including James Clerk Maxwell, who lauded the thesis immediately.
Is it worth your time
Yes. It is the first thermodynamic model to treat fluids as composed of real molecules — not ideal points — and it remains foundational for teaching phase behaviour, critical phenomena, and molecular-scale reasoning in physics and chemistry.
