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SUBJECT-CHEMISTRY


                                            CHAPTER-SURFACE CHEMISTRY


               SUBTOPIC-Adsorption,mechanism of adsorption,differentiate between
               adsorption and absorption.


                KEY NOTES:

                     Adsorption is a surface phenomenon i.e. connection is more in surface than bulk.
                     The substance adsorbed is known as adsorbate and the substance on which adsorption takes
                       place is called adsorbent.
                     The accumulation of molecular species at the surface rather than in the bulk of a
                         solid or liquid is termed adsorption.
                     The process of removing an adsorbed substance from a surface on which it is
                       adsorbed is called desorption.
                     Both adsorption and absorption can take place simultaneously also. The term sorption is used to
                       describe both the processes.
                     Mechanism-Adsorption arises due to the fact that the surface particles of the adsorbentare not
                       in the same environment as the particles inside the bulk. Insidethe adsorbent all the forces
                       acting between the particles are mutuallybalanced but on the surface the particles are not
                       surrounded by atomsor molecules of their kind on all sides, and hence they possess
                       unbalancedor residual attractive forces. These forces of the adsorbent are responsible
                       for attracting the adsorbate particles on its surface.
                     During adsorption, there is always a decrease in residualforces of the surface, i.e., there is
                       decrease in surface energy whichappears as heat. Adsorption, therefore, is invariably an
                       exothermicprocess. In other words, ΔH of adsorption is always negative.
                     During adsorption both ∆H and ∆S are negative.
                                       adsorption                                  absorption
                       1.It is a surface phenomenon.               1. It is a bulk phenomenon.
                       2.Concentration is more on the surface than    2. Concentration is same throughout.
                           bulk phase.
                       3.Its rate is high in the beginning and then    3.Its rate remain same throught out.
                           decreases.
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