The rhs of eq. Figure 6.2 contrasts a potential appropriate for eq. 6.8 with a simple repulsive potential. A freshman chemistry exercise predicts for this system P of atmosphere. Activated charcoal strongly adsorbs most aromatic compounds, including benzene.
Adsorption is well-described by the potential of eq.
6.8 and Fig. Close to the wall, the molecule finds itself in a very deep potential well which, if the kinetic energy of the molecule is not too large, serves to trap the molecule against the container surface. Because adsorption takes place, at equilibrium the benzene pressure inside an activated charcoal container will be much less than expected from the ideal gas equation.