Surface Chemistry Class 12 Notes - Chapter 5

The event of attracting and keeping the molecule of a substance on the surface of a solid is called adsorption. This results in an increased concentration on the surface than in the bulk. The expanse of adsorption of a gas on a solid material depends on the following factors: surface area of the solid, temperature of the gas, nature of the gas, the pressure of the gas, and nature of solid.

  • Adsorbate – The substance that is absorbed. It is held by weak van der Waals forces in physisorption whereas in chemisorption it is held by a strong chemical bond.
  • Adsorbent – The substance on which adsorption occurs.
  • Adsorption isotherm – It is defined as the relationship between the pressure of the gas and extent of adsorption at a constant temperature.

Types Of Catalysis

A substance that enhances the rate of a chemical reaction without getting itself consumed by the reaction is called a catalyst. It does not undergo any change and can be recovered in a chemically unchanged form. The event occurring with a catalyst is known as catalysis.

  • Homogeneous catalysis – When the catalyst and reactants are in the same phase it is called homogeneous catalysis.
  • Heterogeneous catalysis – When the catalyst and reactants are in a different phase it is called heterogeneous catalysis.

Few Important Questions

  1. Explain the difference between absorption and adsorption with an example.
  2. Define lyophobic and lyophilic sols with one example each. Also, explain which sol is easily coagulated and why?
  3. Explain how emulsion is stabilized with emulsifiers. Name any two emulsifiers.
  4. What is aerosol? Write one example
  5. Define enzymes and explain enzyme catalysis mechanism.

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Practise This Question

 Read the assertion and reason carefully to mark the correct option out of the options given below:

(a)If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b)If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c)If assertion is true but reason is false.

(d)If assertion is false but reason is true.
 Assertion : EV(M2+/M) value for copper is positive (+0.34V).
 Reason :  High ionization enthalpy and low heat of hydration energy