Slide 1

  • Topic: Surface Chemistry - Solid surface of on top of which in a liquid with concentration
  • Definition: Surface chemistry deals with the study of chemical reactions which occur at the interface of two phases, usually solid-gas, solid-liquid, or liquid-gas.
  • Importance: It plays a crucial role in various processes like corrosion, catalysis, adsorption, and heterogeneous reactions.
  • Applications: Surface chemistry finds its applications in industries such as paints, petroleum, pharmaceuticals, and pollution control.

Slide 2

  • Adsorption: The process of accumulation of a substance at the surface or interface is called adsorption.
  • Types of adsorption: Physical adsorption (physisorption) and chemical adsorption (chemisorption).
  • Physisorption: Weak forces like Vander Waals forces are responsible for physisorption.
  • Chemisorption: It involves the formation of chemical bonds between the adsorbate and the surface.
  • Examples: Adsorption of gases on activated charcoal, adsorption of dyes on fabrics.

Slide 3

  • Factors affecting adsorption:
    • Nature of the adsorbate and adsorbent.
    • Surface area of the adsorbent.
    • Temperature: Physisorption decreases with increasing temperature, while chemisorption may increase or decrease.
    • Pressure: Physisorption increases with increasing pressure, while chemisorption is usually not affected.

Slide 4

  • Adsorption isotherms: Graphical representation of the variation in the extent of adsorption with pressure at constant temperature.
  • Langmuir adsorption isotherm: The maximum amount of adsorption occurs when the surface is fully covered and no further adsorption is possible.
  • Freundlich adsorption isotherm: The extent of adsorption increases continuously with pressure/ concentration.

Slide 5

  • Catalysis: It is the process where the rate of a chemical reaction is increased by the presence of a substance called a catalyst.
  • Types of catalysis: Homogeneous catalysis and heterogeneous catalysis.
  • Homogeneous catalysis: The catalyst is in the same phase as the reactants.
  • Heterogeneous catalysis: The catalyst exists in a different phase compared to the reactants.

Slide 6

  • Heterogeneous catalysis examples:
    • Haber’s process: N2 + 3H2 ⇌ 2NH3 (using iron as a catalyst).
    • Contact process: 2SO2 + O2 ⇌ 2SO3 (using vanadium pentoxide as a catalyst).

Slide 7

  • Factors affecting catalysis:
    • Nature of the catalyst: It should have high adsorption capacity and the ability to form active intermediates.
    • Surface area: Higher surface area results in increased catalytic activity.
    • Temperature: Generally, the rate of reaction increases with an increase in temperature.
    • Pressure: It depends on the nature of the reactants and products.

Slide 8

  • Activation energy: The minimum amount of energy required to initiate a chemical reaction.
  • Catalyst and activation energy: Catalysts lower the activation energy, making it easier for the reactants to reach the transition state.
  • Reaction coordinate diagram: A graphical representation of the energy changes that occur during a chemical reaction.

Slide 9

  • Contact process: Industrial production of sulfuric acid by the oxidation of sulfur dioxide.
  • Reaction steps:
    • Formation of sulfur trioxide: 2SO2 + O2 ⇌ 2SO3
    • Conversion of sulfur trioxide to sulfuric acid: SO3 + H2SO4 → 2H2S2O7
  • Vanadium pentoxide (V2O5) acts as a catalyst in this process.

Slide 10

  • Benefits of using catalysis in chemical industry:
    • Reduces energy consumption by lowering the operating temperature.
    • Increases the yield of desired products.
    • Selective catalysts can be used to target specific reactions.
    • Reduces the production of unwanted by-products.
    • Enables the recycling and reuse of catalysts, making the process more sustainable.

Slide 11

  • Types of Catalysts:
    • Homogeneous catalysts:
      • Same phase as the reactants.
      • Form temporary complexes with reactants.
      • Example: Acid-catalyzed reactions like esterification.
    • Heterogeneous catalysts:
      • Different phase from the reactants.
      • Reactants are adsorbed onto the surface of the catalyst.
      • Example: Metal catalysts like platinum, nickel, etc.

Slide 12

  • Mechanism of Catalysis:
    • Adsorption:
      • Reactants adsorb onto the surface of the catalyst.
      • Bond formation involving the catalyst.
      • Surface reactions occur.
    • Desorption:
      • Product molecules desorb from the catalyst surface.
      • Released into the bulk phase.
      • Catalyst is regenerated and can be reused.

Slide 13

  • Catalytic Promoters and Inhibitors:
    • Promoters:
      • Enhance the catalytic activity.
      • Increase the rate of the reaction.
      • Examples: Substances like potassium, lead, etc. in catalytic converters.
    • Inhibitors:
      • Reduce the catalytic activity.
      • Decrease the rate of the reaction.
      • Examples: Poisoning of metal catalysts by impurities in the reactants.

Slide 14

  • Catalyst Poisoning:
    • The deactivation of a catalyst by the presence of impurities.
    • Poisoning agents can attach to the active sites of the catalyst.
    • This prevents reactant molecules from adsorbing onto the surface.
    • Examples: Sulfur poisoning of platinum catalysts in automobile exhaust systems.

Slide 15

  • Enzymes as Catalysts:
    • Enzymes are biological catalysts.
    • Highly specific in their actions.
    • Speed up biochemical reactions in living organisms.
    • Examples: Amylase for starch digestion, DNA polymerase for DNA replication.

Slide 16

  • Zeolites as Catalysts:
    • Crystalline, porous materials.
    • Used as shape-selective catalysts.
    • Have a rigid structure with uniform-sized pores.
    • Used in petrochemical industries for cracking hydrocarbons.

Slide 17

  • Surface Indicators:
    • Using indicators to study the surface phenomena.
    • Can detect the presence of specific functional groups.
    • Example: Bromophenol blue for visualizing the adsorption of phenols on minerals.

Slide 18

  • Emulsions:
    • A dispersion of two immiscible liquids.
    • Stabilized by the presence of a surfactant.
    • Example: Mayonnaise (oil in water emulsion).

Slide 19

  • Colloids:
    • Intermediate between true solutions and suspensions.
    • Particles are larger than molecules but smaller than aggregates.
    • Examples: Milk, fog, ink, and paints.

Slide 20

  • Tyndall Effect:
    • Scattering of light by colloidal particles.
    • Makes the path of a beam of light visible.
    • Used to distinguish between true solutions and colloidal dispersions.

Slide 21

  • Colloidal Systems:
    • Dispersed phase: Particles of colloidal size.
    • Dispersion medium: Liquid, gas, or solid.
    • Examples: Sol, gel, foam, aerosol.

Slide 22

  • Types of Colloids:
    • Based on the dispersion medium:
      • Sol: Solid dispersed in a liquid.
      • Gel: Liquid dispersed in a solid.
      • Foam: Gas dispersed in a liquid.
    • Based on the nature of interaction:
      • Lyophilic colloids: Attracted to the dispersion medium.
      • Lyophobic colloids: Repelled by the dispersion medium.

Slide 23

  • Preparation of Colloids:
    • Dispersion methods:
      • Mechanical dispersion: Grinding or milling.
      • Condensation or phase separation: Aggregation or coagulation.
    • Chemical methods:
      • Reduction: Precipitation of metal colloids.
      • Oxidation: Formation of metal oxide or sulfide colloids.
      • Hydrolysis: Formation of metal hydroxide colloids.

Slide 24

  • Properties of Colloids:
    • Brownian motion: Continuous random movement of colloidal particles.
    • Tyndall effect: Scattering of light by colloidal particles.
    • Electrophoresis: Movement of charged colloidal particles in an electric field.
    • Coagulation: Aggregation of colloidal particles to form larger particles.

Slide 25

  • Applications of Colloids:
    • Medicine and healthcare: Drug delivery systems, intravenous fluids.
    • Food industry: Emulsifiers, stabilizers, and thickeners.
    • Cosmetics: Creams, lotions, and shampoos.
    • Environmental science: Treatment of polluted water and air.

Slide 26

  • Emulsions:
    • Definition: Colloidal dispersions of two immiscible liquids.
    • Types of emulsions: Oil-in-water (O/W) and water-in-oil (W/O).
    • Examples: Mayonnaise (oil-in-water) and butter (water-in-oil).

Slide 27

  • Emulsifying Agents:
    • An emulsifier or surfactant is used to stabilize emulsions.
    • Forms a protective layer at the interface of the two immiscible liquids.
    • Examples: Soaps, detergents, and phospholipids.

Slide 28

  • Micelles:
    • Formation of aggregates in certain solutions.
    • Amphiphilic molecules form micelles in water.
    • Hydrophobic tails cluster inside, hydrophilic heads face outside.
    • Used in soap and detergent formulations.

Slide 29

  • Catalytic Converters:
    • Reduce harmful emissions from automobile exhaust.
    • Convert toxic gases like nitrogen oxides (NOx) into less harmful gases.
    • Platinum and palladium act as catalysts in the converter.

Slide 30

  • Summary:
    • Surface chemistry deals with reactions at interfaces.
    • Adsorption can be physical or chemical.
    • Catalysts increase the rate of reactions and can be homogeneous or heterogeneous.
    • Factors like temperature, pressure, and nature of catalyst influence catalysis.
    • Colloids and emulsions have diverse applications in various industries.