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The van der Waals equation corrects the ideal gas law twice: b removes the volume the molecules themselves occupy, and a accounts for their mutual attraction. One mole of a nitrogen-like gas in 0.5 L at 300 K gives 48.6 bar against the ideal 49.9 bar, a compressibility factor just under one because attraction dominates at this density.
van der Waals equation
(P + a n^2 / V^2)(V - n b) = n R T
Compressibility factor
Z = P V / (n R T)
a measures intermolecular attraction, which lowers pressure; b is the excluded volume of the molecules, which raises it by reducing free space.
Near condensation - high pressure or low temperature. Above the critical temperature and below a few bar the ideal law is within a percent.