Van der Waals Equation Calculator
Estimate the pressure of a real (non-ideal) gas using the Van der Waals equation, which accounts for molecular volume and attraction that the ideal gas law ignores.
What This Calculator Does
Real gases don’t perfectly follow the ideal gas law, especially at high pressure or low temperature, because gas molecules actually take up space and attract each other slightly. The Van der Waals equation adds two correction terms to the ideal gas law to model this more realistically.
The Formula
The Van der Waals equation is (P + a·n²/V²)(V − n·b) = nRT, where P is pressure, V is volume, n is moles of gas, T is temperature, R is the universal gas constant, and a and b are substance-specific constants: a accounts for attraction between molecules, and b accounts for the finite volume the molecules themselves occupy. Solving for pressure gives P = nRT/(V − nb) − a·n²/V².
Note: This calculator uses commonly published literature values for a and b and is intended for general educational and planning purposes. It assumes a single pure gas species and does not model mixtures or extreme conditions near a phase transition.