van der Waals (pressure)

The van der Waals equation is based on a modification of the ideal gas law and approximates the behavior of real fluids, taking into account the nonzero size of molecules and the attraction between them.

The equation uses the following state variables: the pressure of the fluid, total volume of the container containing the fluid, number of moles, and absolute temperature of the system.  The van der Waals and the ideal gas equation both have the same form.  van der Waals modified the pressure and volume factors with the inclusion of the a nd b coefficients.  The parameter a is called the proportionality constant and provides a measure of how strongly the molecules attract each other.  van der Waals reasoned that the intermolecular atrractive forces would have an influence on the pressure.  The parameter b, is called the excluded volume per mole. This has an effect on the volume parameter because the volumes of the molecules in the gas are not point masses, and therefore there volume is excluded from the volume of the container.