Adsorption – Class 12 | Chapter – 5 | Surface Chemistry | Chemistry Short Notes Series PDF for NEET & JEE

Adsorption: Adsorption is a fundamental process in surface chemistry where molecules or ions from a gas or liquid phase adhere to the surface of a solid or liquid. The substance that is adsorbed is called the adsorbate, and the surface on which it accumulates is known as the adsorbent. This phenomenon is crucial in various scientific and industrial applications, including catalysis, gas purification, chromatography, and chemical sensors, among others.

Types of Adsorption

There are two main types of adsorption:

  • Physisorption (Physical Adsorption): Physisorption occurs due to weak van der Waals forces or London dispersion forces between the adsorbate and adsorbent. The interaction is primarily driven by intermolecular forces and does not involve the formation of chemical bonds. As a result, physisorption is generally a reversible process and sensitive to changes in temperature and pressure.
  • Chemisorption (Chemical Adsorption): Chemisorption, on the other hand, involves the formation of chemical bonds between the adsorbate and adsorbent. This type of adsorption typically requires more energy than physisorption and is often specific to certain chemical species. Chemisorption tends to be more stable and less affected by temperature and pressure changes compared to physisorption.

Factors Affecting Adsorption

Several factors influence the process of adsorption:

  • Surface area: A larger surface area of the adsorbent provides more active sites for adsorption to occur, leading to higher adsorption capacity.
  • Temperature: Adsorption is often favored at low temperatures for physisorption and moderate temperatures for chemisorption. An increase in temperature can lead to desorption.
  • Pressure: Higher pressures can enhance adsorption, especially for gas-phase adsorbates.
  • Nature of the adsorbate and adsorbent: The chemical properties of both the adsorbate and adsorbent play a crucial role in determining the strength and specificity of the adsorption process.
  • Concentration: Higher concentrations of the adsorbate in the surrounding medium can increase adsorption.

Applications of Adsorption

Adsorption has numerous applications across various fields, including:

  • Catalysis: Adsorption plays a vital role in catalytic processes, where reactants are adsorbed onto a catalyst surface, facilitating chemical reactions.
  • Gas purification: Adsorption is used to remove impurities and pollutants from gases, such as in air purifiers and industrial gas purification processes.
  • Chromatography: In analytical chemistry, adsorption is employed in techniques like column chromatography to separate and analyze different components of a mixture.
  • Chemical sensors: Adsorption-based sensors can detect and measure specific substances by monitoring changes in adsorption behavior.
  • Water purification: Adsorption is used in water treatment to remove contaminants like heavy metals and organic pollutants.

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By Team Learning Mantras