Question

(a)i. Name five common feautures of catalysis ii. Describe adsorption, desorption, physisorption and chemisorption. (b) Draw a labeled phase diagram for water and explain it briefly.

Answer 1

a) i)

1. The catalyst remains unchanged (in mass and chemical composition ) in the reaction (Activity of catalyst.)

2. A small quantity of the catalyst is required. e.g. One mole of colloid Pt catalyses

3. The catalyst does not change the equilibrium constant. But the equilibrium approaches earlier.

4. Specificity of Catalyst:

The catalyst is specific in nature. It means by the change of catalyst, nature of the products changes or specific catalyst for a specific reaction.

Or

5. The catalyst can not make impossible reaction to occur and does not intiate a reaction.

a) ii)

:Chemisorption (or chemical adsorption) is adsorption in which the forces involved are valence forces of the same kind as those operating in the formation of chemical compounds.

:Physisorption (or physical adsorption) is adsorption in which the forces involved are intermolecular forces (van der Waals forces) of the same kind as those responsible for the imperfection of real gases and the condensation of vapours, and which do not involve a significant change in the electronic orbital patterns of the species involved.

:Adsorption is a surface process, the accumulation of a gas or liquid on a liquid or solid. Adsorption can be defined further based on the strength of the interaction between the adsorbent (the substrate onto which chemicals attach) and the adsorbed molecules.

:Desorption is the release of one substance from another, either from the surface or through the surface. Desorption can occur when an equilibrium situation is altered. Imagine a tank of water in equilibrium with its surroundings. The amount of oxygen entering and leaving the water from the air will be the same — and the oxygen concentration in the water will be constant. If the water temperature increases, the equilibrium and solubility are changed, and the oxygen will desorb from the water — lowering the oxygen content.

(b)

Phase Diagram for Water :

Water is a unique substance in many ways. One of these special properties is the fact that solid water (ice) is less dense than liquid water just above the freezing point. The phase diagram for water is shown in the Figure below .

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