The achievement of equilibrium on a small surface displays the following pattern:

Some passing molecules will condense on the surface (physical as opposed to chemical absorption).

After some finite time the molecule may acquire sufficient energy to leave and be replaced by another.

After sufficient time, a state of equilibrium will be reached wherein the number of molecules leaving the surface will equal the number arriving.

The number of molecules on the surface is a function of:

• The nature of the adsorbent
• The nature of the molecule being adsorbed(the adsorbate)
• The temperature of the system and concentration of the adsorbate over the adsorbent surface