Question

Which of the following is correct regarding the Langmuir's model of adsorption of a gas on a solid surface?

• A. The rate of desorption of adsorbed molecules from the surface does not depend on the surface covered
• B. The adsorption at a single site on the surface may involve multiple molecules at the same time
• C. The mass of gas striking a given area of surface is proportional to the pressure of the gas
• D. The mass of gas striking a given area of surface is independent of the pressure of the gas

Answer 1

The correct option is C The mass of gas striking a given area of surface is proportional to the pressure of the gas

Langmuir adsorption is basically a type of chemisorption, i.e., chemical bonds exist between the adsorbate & adsorbent.

• A is incorrect as the rate of desorption (removal of adsorbate from adsorbent) is equal to the rate of adsorption at equilibrium and chemical adsorption depends on the number of available sites on the surface.

• Chemisorption is always a unimolecular layer because there exists a strong bonding between a single adsorbate & adsorbent site. Multiple molecules cannot involve in bond formation at the same adsorbent site.

• According to Langmuir adsorption isotherm $\frac{x}{m}=\frac{ap}{1+bp}$ ,where a and b are two Langmuir parameters. x is the mass of adsorbate, m is mass of adsorbent and $\frac{x}{m}$ is the extent of adsorption.

• The extent of adsorption depends on the mass of adsorbate which directly depends on its pressure.