How this calculator works
The van der Waals model corrects ideal-gas pressure for molecular attraction and excluded volume. Constants are specific to each gas, and the molar volume must exceed b. The presets convert the cited table into SI units. The model is approximate and can fail near phase coexistence or dense states. Pressure or temperature is determined directly; this tool does not choose a phase from the cubic volume equation.
Formula
(P + a/Vm²)(Vm - b) = RT; P = RT/(Vm - b) - a/Vm²; Vm = V/n; Z = P Vm/(RT).
Worked example
With custom a = b = 0, 1 mol at 300 K in 0.01 m³ gives 249433.879 Pa, matching the ideal-gas law. With 2 mol in 0.01 m³ at 166289.252 Pa and zero corrections, temperature is 100 K.
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Frequently asked questions
What units do the custom constants use?
Use Pa m⁶/mol² for a and m³/mol for b. A table in bar L²/mol² and L/mol needs conversion.
Why must molar volume exceed b?
The available-volume term Vm - b must be positive. At or below b the gas-state formula is invalid.
Does the model predict condensation reliably?
It captures qualitative nonideal behaviour, but detailed phase equilibrium needs a suitable equation of state and phase-stability treatment.