UPSC Exam  >  UPSC Notes  >  Chemistry Optional Notes for UPSC  >  Adsorption Isotherms: Freundlich, Langmuir, and BET

Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC PDF Download

Adsorption Isotherm

  • Adsorption isotherms have been of immense importance to research dealing with environmental protection and adsorption techniques. The two primary methods used for predicting the adsorption capacity of a given material are known as the Freundlich and Langmuir isotherms.
  • An adsorption isotherm is a graph that represents the variation in the amount of adsorbate(x) adsorbed on the surface of the adsorbent with the change in pressure at a constant temperature.
    Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC
  • As we know from Le Chatelier’s principle, the direction of equilibrium in a reaction shifts in the direction in which stress is relieved. So, here we can see that upon application of excess pressure on the system, the equilibrium shifts in the direction where the number of molecules decreases so that the pressure in the system decreases.
  • From the graph, we also observe that after attaining a pressure Ps, that is the saturation pressure, the variation in the amount of adsorbent adhering to the adsorbate becomes zero. This happens because the surface area available for adsorption is limited and as all the sites are occupied, a further increase in pressure does not cause any difference.
  • Different adsorption isotherms have been proposed by different scientists namely,
    • Langmuir isotherm
    • Freundlich isotherm
    • BET theory
  • The graph shown above shows the isotherm proposed by Freundlich.

Question for Adsorption Isotherms: Freundlich, Langmuir, and BET
Try yourself:
Which of the following methods is used for predicting the adsorption capacity of a given material?
View Solution

1 Crore+ students have signed up on EduRev. Have you? Download the App

Freundlich Adsorption Isotherm

Freundlich adsorption gives the variation in the quantity of gas adsorbed by a unit mass of solid adsorbent with the change in pressure of the system for a given temperature. The expression for the Freundlich isotherm can be represented by the following equation:
Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC
where n>1
Where x is the mass of the gas adsorbed, m is the mass of the adsorbent, P is the pressure and n is a constant which depends upon the nature of the adsorbent and the gas at a given temperature. Taking the logarithm on both the sides of the equation, we get,
Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC
The plot of this equation is a straight line as represented by the following curve.
Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC

Langmuir Adsorption Isotherms

The Freundlich adsorption isotherm is followed by another two isotherms, Langmuir adsorption isotherms and BET theory. The Langmuir adsorption isotherms predict linear adsorption at low adsorption densities and a maximum surface coverage at higher solute metal concentrations.
The Langmuir adsorption isotherm has the form:
Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC
Where

  • θ is the fraction of the surface covered by the adsorbed molecule.
  • K is an equilibrium constant known as the adsorption coefficient.
  • { K= ka/kd = rate constant for adsorption/ rate constant for desorption}
  • p is the pressure.

The Langmuir adsorption is applicable for monolayer adsorption onto a homogeneous surface when no interaction occurs between adsorbed species.

Download the notes
Adsorption Isotherms: Freundlich, Langmuir, and BET
Download as PDF
Download as PDF

BET Adsorption Isotherm

  • The theory of multilayer adsorption proposed by Brunauer, Emmett and Teller in 1938 (BET Theory) assumes that physisorption results in the formation of multilayer adsorption. The theory also assumes that the solid surface has uniform sites of adsorption and that adsorption at one site does not affect adsorption at neighbouring sites.
  • After the formation of the monolayer, the adsorption process can continue with the formation of the multilayer involving the second layer, third layer and so on.
  • The equation for BET is
    Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC

Question for Adsorption Isotherms: Freundlich, Langmuir, and BET
Try yourself:
Which adsorption isotherm assumes the formation of multilayer adsorption?
View Solution

Take a Practice Test
Test yourself on topics from UPSC exam
Practice Now
Practice Now

Applications of Adsorption

Following are the applications of adsorption:

  • Gas masks: Poisonous gases get adsorbed at the surface of the mask and prevent its encounter when used by coal miners.
  • Production of vacuum: Traces of air are adsorbed on charcoal and removed from devices undergoing the process of evacuation.
  • Removal of moisture: Silica gel pellets are used for the adsorption of moisture in medicines and new plastic bottles in order to control humidity.
  • Removal of colour: The juice extracted from cane is treated with animal charcoal for the removal of the colouring agent in order to get a clear liquid solution.
  • As Catalysts: Suitable materials are used as a catalyst such that reactants get adhered to its surface, thus enabling the reaction to proceed at a faster rate and increasing the rate of reaction.
The document Adsorption Isotherms: Freundlich, Langmuir, and BET | Chemistry Optional Notes for UPSC is a part of the UPSC Course Chemistry Optional Notes for UPSC.
All you need of UPSC at this link: UPSC
Are you preparing for Exam? Then you should check out the best video lectures, notes, free mock test series, crash course and much more provided by EduRev. You also get your detailed analysis and report cards along with 24x7 doubt solving for you to excel in exam. So join EduRev now and revolutionise the way you learn!
Sign up for Free Download App for Free
308 docs

Up next

FAQs on Adsorption Isotherms: Freundlich, Langmuir, and BET - Chemistry Optional Notes for UPSC

1. What is an adsorption isotherm?
Ans. An adsorption isotherm is a mathematical equation that describes the relationship between the amount of adsorbate (substance being adsorbed) and the concentration of adsorbate in the adsorbent (solid material on which adsorption occurs) at a constant temperature.
2. What is the Freundlich adsorption isotherm?
Ans. The Freundlich adsorption isotherm is an empirical equation that is often used to describe the adsorption of gases or solutes onto solid surfaces. It states that the amount of adsorbate adsorbed is directly proportional to the equilibrium concentration of the adsorbate raised to a power.
3. What is the Langmuir adsorption isotherm?
Ans. The Langmuir adsorption isotherm is a model that describes the adsorption of gases or solutes onto a solid surface. It assumes that the adsorption occurs on a homogeneous surface with a fixed number of identical adsorption sites. The equation predicts that the amount of adsorbate adsorbed is proportional to the equilibrium concentration of the adsorbate divided by the sum of the equilibrium concentration and a constant.
4. What is the BET adsorption isotherm?
Ans. The BET (Brunauer-Emmett-Teller) adsorption isotherm is a model commonly used to describe the physical adsorption of gases onto a solid surface. It is based on the assumption that multiple layers of adsorbate molecules can form on the surface. The equation predicts a monolayer adsorption capacity and provides information about the surface area of the adsorbent material.
5. What are some applications of adsorption?
Ans. Adsorption has various applications, including: - Water treatment: Adsorption is used to remove pollutants and contaminants from water, such as heavy metals, organic compounds, and dyes. - Gas separation: Adsorption processes are employed to separate gases, such as nitrogen and oxygen, from air or to remove impurities from natural gas. - Catalysis: Adsorption plays a crucial role in catalytic reactions, where reactant molecules are adsorbed onto a catalyst surface, leading to increased reaction rates. - Drug delivery: Adsorption is used in drug delivery systems to control the release of drugs from carriers, ensuring controlled and targeted delivery. - Environmental remediation: Adsorption is utilized to remove pollutants from soil and air, helping to clean up contaminated sites and improve air quality.

Up next

Explore Courses for UPSC exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Sample Paper

,

Free

,

Adsorption Isotherms: Freundlich

,

and BET | Chemistry Optional Notes for UPSC

,

Summary

,

practice quizzes

,

Viva Questions

,

study material

,

and BET | Chemistry Optional Notes for UPSC

,

MCQs

,

Important questions

,

Langmuir

,

and BET | Chemistry Optional Notes for UPSC

,

Semester Notes

,

mock tests for examination

,

Objective type Questions

,

Extra Questions

,

Exam

,

Langmuir

,

ppt

,

Adsorption Isotherms: Freundlich

,

Adsorption Isotherms: Freundlich

,

Langmuir

,

video lectures

,

past year papers

,

shortcuts and tricks

,

Previous Year Questions with Solutions

,

pdf

;