Van der Waals Calculator

The Van der Waals equation

The ideal gas law PV = nRT assumes gas particles have no volume and no intermolecular attraction. The Van der Waals equation corrects both assumptions: the term a(n/V)² accounts for attractive forces between molecules, and the term nb accounts for the finite volume of the molecules themselves.

For gases at high pressure or low temperature — where real behaviour deviates most from ideal — the Van der Waals equation gives substantially more accurate results. The constants a and b are specific to each gas and are determined experimentally.

When to use Van der Waals vs ideal gas law

For most everyday calculations at moderate temperatures and pressures, the ideal gas law is sufficient. Use the Van der Waals equation when working with gases near their condensation point, at high pressures (above ~10 atm), or when accuracy beyond a few percent matters.