Now, the number of molecules striking the surface will be proportional to the concentration (c), the fraction of exposed surface (1-a) and some constant (a), thus,

n' = ac(1-a) (27)

Similarly, the number of molecules leaving the surface will be proportional to the area covered and another constant (b)

n" = ba (28)

(b) is related to the probability of any molecule of solvent (B) having sufficient kinetic energy to overcome the molecular interactions between solvent (B) and the stationary phase surface and thus, escape from the surface

Equating (27) and (28),

ba = ac(1-a)

(29)

Equation (29) is the function that describes the Langmuir Isotherm.