Surface Chemistry

Definition

  • Surface chemistry is the branch of chemistry that deals with the study of phenomena occurring at the surfaces or interfaces of materials.

Importance

  • Interfaces and surfaces play a crucial role in various applications such as catalysis, heterogeneous reactions, adsorption, etc.
  • Understanding surface chemistry is essential for developing new materials and improving existing technologies.

Adsorption

  • Adsorption is the process by which molecules or ions are attracted to and accumulate on a solid surface.
  • Types of adsorption:
    • Physical adsorption (physisorption)
    • Chemical adsorption (chemisorption)

Factors Affecting Adsorption

  • Nature of the adsorbate and adsorbent.
  • Temperature and pressure.
  • Surface area of the adsorbent.
  • Activation energy of the adsorption process.

Types of Adsorption Isotherms

  • Langmuir Adsorption Isotherm
  • Freundlich Adsorption Isotherm
  • BET Adsorption Isotherm
  • Tempkin Adsorption Isotherm

Catalysis

  • Catalysis is the process of increasing the rate of a chemical reaction by using a substance called a catalyst.
  • Types of catalysis:
    • Homogeneous catalysis
    • Heterogeneous catalysis
    • Enzyme catalysis

Enzyme Catalysis

  • Enzymes are biological catalysts that speed up chemical reactions in living organisms.
  • Properties of enzymes:
    • Highly specific
    • Can be reused
    • pH and temperature sensitive

Zeolites

  • Zeolites are crystalline inorganic solids composed of aluminum, silicon, and oxygen atoms.
  • Properties of zeolites:
    • High surface area
    • Selective adsorption and separation properties
    • Catalytic properties

Classification of Catalysis

  • Classification based on the mechanism:
    • Acid catalysis
    • Base catalysis
    • Redox catalysis
  • Classification based on the type of reactants:
    • Homogeneous catalysis
    • Heterogeneous catalysis

Catalytic Promoters and Inhibitors

  • Catalytic promoters enhance the activity of catalysts and increase their efficiency.
  • Catalytic inhibitors reduce the activity of catalysts and decrease their efficiency.
  • Examples of catalytic promoters and inhibitors in industrial processes.

Examples of Catalytic Reactions

  • Haber process (nitrogen fixation)
  • Contact process (sulfuric acid production)
  • Oil refining industry
  • Automotive catalytic converters

Note: Please continue with the next set of slides.

Langmuir Adsorption Isotherm

  • Proposed by Irving Langmuir in 1916.
  • Describes adsorption as a monolayer formation on a solid surface.
  • Assumptions:
    • Adsorption occurs on a specific site on the surface.
    • Attractive forces between the adsorbate molecules are negligible.

Langmuir Adsorption Isotherm (contd.)

  • Equation: Langmuir equation where:
    • x/m is the fraction of the adsorbent surface covered by adsorbate
    • C is the equilibrium concentration of the adsorbate in the solution
    • Ka is the equilibrium constant of adsorption

Freundlich Adsorption Isotherm

  • Proposed by Herbert Freundlich in 1909.
  • Describes adsorption on a heterogeneous surface with multiple adsorption sites.
  • Equation: Freundlich equation where:
    • x is the amount of adsorbate adsorbed on the surface
    • C is the equilibrium concentration of the adsorbate in the solution
    • KF and n are constants

Freundlich Adsorption Isotherm (contd.)

  • Graphical representation of Freundlich isotherm is non-linear.
  • The value of n indicates the intensity of adsorption.
  • If n > 1, adsorption is favorable.
  • If n = 1, adsorption is linear.
  • If n < 1, adsorption is unfavorable.

BET Adsorption Isotherm

  • Proposed by Stephen Brunauer, Paul H. Emmett, and Edward Teller in 1938.
  • Describes the multilayer adsorption on a solid surface.
  • Assumes that adsorption occurs in layers up to a certain thickness.

BET Adsorption Isotherm (contd.)

  • Equation: BET equation where:
    • x/m is the fraction of the adsorbent surface covered by adsorbate
    • C is the equilibrium concentration of the adsorbate in the solution
    • K, n, and B are constants

Tempkin Adsorption Isotherm

  • Proposed by M. Tempkin and V. Pyzhev in 1940.
  • Describes the reversible physical adsorption process.
  • Assumes a decrease in the heat of adsorption with the increase in the coverage of the adsorbate.

Tempkin Adsorption Isotherm (contd.)

  • Equation: Tempkin equation where:
    • x is the amount of adsorbate adsorbed on the surface
    • C is the equilibrium concentration of the adsorbate in the solution
    • R is the gas constant
    • T is the temperature
    • B and Kt are constants

Applications of Surface Chemistry

  • Catalysis in industries like petroleum refining, plastics production, and pharmaceuticals.
  • Photocatalysis for water splitting and pollutant degradation.
  • Adsorption for water and air purification.
  • Surface coatings to improve the efficiency and durability of materials.

Review Questions

  • What is the difference between physical adsorption and chemical adsorption?
  • Explain the Langmuir adsorption isotherm and its assumptions.
  • How does the Freundlich adsorption isotherm describe heterogeneous surfaces?
  • Discuss the assumptions and equation of the BET adsorption isotherm.
  • What is the Tempkin adsorption isotherm and how does it differ from other isotherms? Sure! Here are slides 21 to 30 in markdown format:

Factors Affecting Catalysis

  • Nature of catalyst and reactants.
  • Surface area and particle size of the catalyst.
  • Temperature and pressure.
  • Presence of catalyst promoters or inhibitors.
  • pH of the reaction medium.

Homogeneous Catalysis Examples

  • Acid-catalyzed ester hydrolysis.
  • Base-catalyzed alcohol dehydrogenation.
  • Transition metal complex-catalyzed oxidation reactions.

Heterogeneous Catalysis Examples

  • Hydrogenation of unsaturated hydrocarbons on a metal catalyst.
  • Haber process for ammonia synthesis using an iron catalyst.
  • Oxidation of sulfur dioxide to sulfur trioxide using a vanadium pentoxide catalyst.

Automotive Catalytic Converters

  • Convert harmful gases emitted by vehicles (like carbon monoxide, nitrogen oxides, and hydrocarbons) into less harmful substances.
  • Consist of a catalyst coated with platinum, palladium, and rhodium.
  • Chemical reactions involved: oxidation and reduction reactions.

Langmuir-Hinshelwood Mechanism

  • Proposed by Irving Langmuir and E. K. Hinshelwood.
  • Describes the mechanism of reaction occurring on the surface of a solid catalyst.
  • Steps involved:
    • Adsorption of reactants on the catalyst surface.
    • Formation of an activated complex.
    • Surface reaction to form products.
    • Desorption of products from the surface.

Eley-Rideal Mechanism

  • Proposed by Derek Barton and Michael Eley.
  • Describes a reaction between a gas-phase reactant and an adsorbed reactant on the catalyst surface.
  • Steps involved:
    • Adsorption of gas-phase reactant on the catalyst surface.
    • Reaction between the adsorbed reactant and the gas-phase reactant.
    • Desorption of the products from the surface.

Colloids

  • Colloids are a type of dispersion in which particles are dispersed in a continuous medium.
  • Types of colloids:
    • Sol: solid dispersed in a liquid medium.
    • Gel: liquid dispersed in a solid medium.
    • Emulsion: liquid dispersed in another liquid.
    • Foam: gas dispersed in a liquid or solid.

Types of Colloids

  • Based on the nature of dispersed phase and continuous phase:
    • Lyophilic colloids: dispersed phase has an affinity for the continuous phase.
    • Lyophobic colloids: dispersed phase does not have an affinity for the continuous phase.
  • Based on the particle size:
    • Micelles: colloidal clusters of molecules.
    • Macromolecular colloids: large molecules dispersed in a solvent.

Emulsions

  • Emulsions are colloidal suspensions of one liquid dispersed in another immiscible liquid.
  • Types of emulsions:
    • Oil-in-water emulsion: oil droplets dispersed in water.
    • Water-in-oil emulsion: water droplets dispersed in oil.
  • Examples: mayonnaise, milk, lotions.

Applications of Colloids

  • Food industry (e.g., stabilizing creaminess of ice cream).
  • Pharmaceutical industry (e.g., drug delivery systems).
  • Photography (e.g., development of photographs).
  • Paints and coatings industry (e.g., color dispersion and stability).

I hope these slides are helpful for your lecture on surface chemistry for 12th Boards chemistry.