Surface Chemistry Conclusion

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Adsorption is a surface phenomenon. In this process there is accumulation of a substance on the surface of a solid or a liquid as compared to the bulk of the solid or liquid. The substance which is adsorbed is called the adsorbate and the substance on to whose surface the adsorbate is adsorbed is called the adsorbent. In physisorption, adsorbate is held to the adsorbent by weak van der Waals' forces, and in chemisorption, the forces of attraction between the adsorbate and the adsorbent are chemical bond forces. All solids have the potential to adsorb gases. The extent of adsorption of a gas on a solid depends on the nature of the gas, nature of the solid, specific area of the solid, pressure of gas, temperature at which adsorption occurs, and activation of the adsorbent. Adsorption isotherm describes the relationship between the extent of adsorption and pressure of gas for a given temperature. Adsorption isobar gives the relationship between the extent of adsorption and temperature for a given pressure of gas.

Catalysis involves reactions where catalysts are used. Catalysts are used to accelerate the rate of reaction. Catalysts accelerate the rate of reaction by providing an alternate reaction pathway in which the activation energy is lower. Homogenous catalysis involves catalysts which are of the same phase as the reactants. Heterogeneous catalysis involves catalysts which are in a different phase than the reactant. Heterogeneous catalysis using solid catalysts have immense use in industrial processes. Enzymes, which are usually proteins, catalyze reactions in physiological systems. Enzymes are characterized by their immense catalytic power and specificity. Enzymes bind substrate to specific binding sites called active sites. Without, enzymes, most physiological reactions will not occur at perceptible rates.

Colloidal solutions are intermediate between true solutions and suspensions. Colloidal particles sizes fall in the range of 10 A^o to 10000 A^o. Colloidal system is biphasic. It consists of the dispersed phase and the dispersion medium. Colloidal system are classified in three ways depending on:

i) Physical states of the dispersed phase and dispersion medium nature of interaction between the dispersed phase and the dispersion medium.

ii) Colloidal systems exhibit their characteristic optical, mechanical and electrical properties. Colloids can be destabilized by the process of coagulation. Emulsions are colloids in which both the phases are liquids. Emulsions are of two types, namely

a) oil-in-water type and

b) water-in-oil type.

The process of making emulsions is called emulsification. Emulsions are stabilized by adding emulsifying agents or stabilizers. Colloids have wide ranging uses.

iii) Nature of particles of the dispersed phase.