Van der Waals equation

Equation of state for a fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle force (such as the van der Waals force.) It was derived by Johannes Diderik van der Waals in his doctoral thesis (Leiden 1873), based on a modification of the ideal gas law. The importance of his work was the recognition that the gas and liquid phase of a compound transform continuously into each other. Above the critical temperature there is even no difference between the gas and the liquid phase, which is why it is proper to speak of the equation of a fluid, a generic term for liquid and gas.

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Formula

\left(P+\frac {a}{V^{2}_{m}}\right)\left(V_{m}-b\right)=RT where P is the gas pressure (Pa), n the amount of substance (mol), V the gas volume (m3), R the perfect gas constant, b the volume to be substracted for one mole and α a proportionnality coefficient.