In Freundlich adsorption isotherm, the value of 1/n is:

Concept:

Adsorption:

• Adsorption is defined as the deposition of molecular species onto the surface.
• The molecular species that gets adsorbed on the surface is known as Adsorbent and the surface on which adsorption occurs is known as Adsorbate.
• It is a surface phenomenon and occurs due to the unsaturation of forces on the surface of an adsorbate molecule.

​

• There are two types of adsorption:
  • Physical or physisorption where there exist only weak van der Waals forces between adsorbent and adsorbate.
  • Chemical or chemisorption where new bonds are formed between adsorbent and adsorbate.

Explanation: 

• In adsorption isotherms, the fraction of moles of adsorbate (x) by the grams of adsorbent(m) versus P is plotted.
• The Freundlich isotherm gives us the empirical relationship between the amount of gas adsorbed and its equilibrium pressure P.
• It is seen that the amount of adsorption increases with an increase of pressure when the pressure is in the lower range.
• As the pressure increases, the rate of adsorption increases but reaches saturation after some point.
• After this point, the amount of adsorption doesn't change even when pressure is increased.
• The equation of Freundlich isotherm is given as follows:

\(\frac{{\rm{x}}}{{\rm{m}}} \propto {\rm{\;}}{{\rm{P}}^{\frac{1}{{\rm{n}}}}}\) where k and n are constant for a particular adsorbent and adsorbate at a fixed temperature.

• The graph is represented as follows.

• When the temperature is fixed and pressure is low, the adsorption becomes directly proportional to the pressure of the gas.
• The relation reduces to
• x=kP.

This signifies, 1/n = 1 or n = 1.

• At a higher range of pressure, the adsorption becomes independent of pressure and the equation reduces to

x/m= k.

We can infer from this that 1/n = 0.

Hence, in Freundlich adsorption isotherm, the value of 1/n is 0 to 1.