Van der Waals equation of state

The van der Waals equation is

$\left.p={\frac {nRT}{V-nb}}-a\left({\frac {n}{V}}\right)^{2}\right.$.

where:

• $p$ is the pressure

• $V$ is the volume

• $n$ is the number of moles

• $T$ is the absolute temperature

• $R$ is the Gas constant; $R=N_{A}k_{B}$, with $N_{A}$ being Avogadro constant

The van der Waals equation of state takes into account two features that are absent in the ideal Gas equation of state:

The parameter $b$ introduces somehow the repulsive behavior between pairs of molecules at short distances, it represents the minimum molar volume of the system.

whereas $a$ measures the attractive interactions between the molecules

The van der Waals equation of state leads to a liquid-vapor equilibrium at low temperatures, with the corresponding critical point