Johannes van der Waals

Van der Waals equation

Van der Waals’s 1873 equation was the first thermodynamic model to treat fluids as composed of real molecules — with finite size and mutual attraction — and it successfully described both liquid and gas phases, predicted critical-point behaviour, and yielded quantitative estimates of molecular size and attraction strength. It did not prove molecular existence, nor does it hold across all conditions. Its value lies in making molecular assumptions productive — long before they were directly observable.