Page 1 : forces., 2. Not specific in nature, All, all solids. For example, all gases adsorb on, charcoal., , , , , ange 20 - 40 kJ mol!, 4, Occurs at the low temperature and, decreases with an increase of temperature., , , , , , , physically adsorbed on ‘iron., , , , 6. Reversible, , 1L4 Factors affecting adsorption of gases, om solids : All solids adsorb gases to some, extent. The extent of adsorption depends upon, a number of factors discussed in this section., i. Nature of adsorbate (gas) :(The amount, of gas adsorbed by a solid depends on the, nature of the gas. Gases having high critical, temperatyre liquify easily and can readily be, adsorbed. Refer to chapter 10), The gases such, as SO,, Cl, NH, which are easily liquifiable, are adsorbed to a large extend compared to N.,, ‘O,, H, ete, which are difficult to liquify. i, , Table 11.3 : Critical temperature of gasés and, volume adsorbed, , rs, , , , , , | $0, | ere, 2. Nature of adsorbent:{ Substances which, provide large surface area for a given mass are, effective as adsorbents and adsorb appreciable, volumes of gases. Silica gel, charcoal are, effective adsorbents due to their porous nature"|, , , , , , gases adsorb on 2. Highly specific, , , , 3. The heat of adsorption is low and lies in the 3., , , , , 5. For example ; at low temperature N, gas is | 5, , , , 6. Irreversible., , Physisorbed layer may be multimolecular layer, of | 7. Chemisorption, , 7., adsorbed particles under high pressure., , , , ‘and occurs only when chemi,, is possible between adsorbe,, For example, adsorption, , drogen on nickel, etc, , , , bond formation, and adsorbate., , , , , , , , , , , , , 2 high temperature, the exten) i, ay, , * chemical adsorption is lowered at very hi:, , ature, due to bond breaking., For example N, gas chemically adsorbed ,, , iron at high temperature forms a Jayer of iror, nitride, which desorbs at ve high temperature, , , , , , , , forms monomolecular laye, adsorbed particles., 3. Surface area of adsorbent fAdsorp' 0, a surface phenomenon. Hence, the extent, adsorption increases with increase in surfa, area of adsorbent] Finely divided substance, rough surfaces, colloidal substances are g, adsorbents as they provide larger surface are, for a given mass., 4. Temperature, , , , 3 [Adsorption is, , exothermic process. According to LeChatelier’s principle (Chapter 12), it, , favoured at low temperature. The amount o, gas adsorbed is, thus, inversely proportiona, to temperature. J =, Figure 11.2 shows plots of volume of \, adsorbed per unit mass of adsorbent against, the pressure of a gas at different temperatures, As temperature increases from 193 K to 273, K at a constant pressure ‘P’ the amount of gas, adsorbed decrease., 5. Pressure of gas -{ At any temperature, the extent of gas adsor increases with an, increase of pressure\The extent of adsorption, is directly proportional to Pressure of the gas, Athigh pressures extent of adsorption becomes, independent of the pressure. The surface of, adsorbent is, then, almost fully covered by, adsorbed gaseous molecules., , a