Chemistry - Real Gas Question with Solution | TestHub

The van der Waals equation was proposed in 1873. It was a first step towards taking into account interaction forces between real gas molecules. The perfect-gas equation refers to point-like particles which do not interact with one another. The b correction accounts for real gas molecules moving in only part of the occupied volume, obtained by subtracting the molecules’ own volume. The correction $a/V_m^2$, proportional to the square of density, accounts for attraction between gas molecules. At the critical point, $(\partial P/\partial V_m{)}_T=0$ and $({\partial }^{2}P/\partial V_m^2{)}_T=0$. The equation can be made dimensionless using $P_r=P/P_c,T_r=T/T_c,V_r=V_m/V_c$. In these coordinates, $(P_r+3/V_r^2)(3V_r-1)=8T_r$.