Adsorption The phenomenon of higher concentration of any molecular species at the surface than in the bulk Adsorbent ID: 1021066
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1. SURFACE CHEMISTRY
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3. AdsorptionThe phenomenon of higher concentration of any molecular species at the surface than in the bulk AdsorbentThe substance on the surface of which adsorption takes place is called adsorbent AdsorbateThe substance which is being adsorbed on the surface of another substance. DesorptionThe process of removal of an adsorbed substance from the surface on which it is absorbed
4. Activated CarbonActivated AluminaSilica GelMolecular Sieves (Zeolites)Polar and Non-polar adsorbentsAdsorbent Materials
5. Adsorption vs absorption
6. Types of AdsorptionPositive adsorption occurs when the concentration of adsorbate is higher on the surface of adsorbent than in the bulk. Negative adsorption occurs when the concentration of adsorbate is less on the surface of adsorbent than in the bulk.
7. Types of adsorptionPhysical adsorptionChemical adsorption
8. Factors affecting adsorptionEffect of adsorbate: The easily liquifiable gases like NH3, HCl, CO2 etc. are adsorbed to a greater extent than the permanent gases such as H2 ,O2, N2, etc.Effect of specific area of the absorbent: The greater the specific area of the solid, the greater would be its adsorbing capacity.Effect of temperature:adsorption decreases with increase in temperature.Effect of pressure: An increase in pressure causes an increase in the magnitude of adsorption of an adsorbent.
9. Over a narrow range of pFreundlich IsothermA graph between the amount (x/m) adsorbed by an adsorbent and the equilibrium pressure of the adsorbate at constant temperature is called adsorption isothermAt low pressure the graph is nearly straight lineAt high pressure x/m becomesindependent of p
10. Freundlich Isotherm
11. Langmuir adsorption isotherm:The values of constants ‘a’ and ‘b’ depend upon the nature of adsorbate, nature of solid adsorbent and temperature.a = ka x ka’/kdb = ka/kdCombining equations (1) and (2):
12. Summary of adsorption isotherms Easy to fit adsorption dataChemisorptions and physisorptionFreundlichUseful in analysis of reaction mechanismChemisorption and physisorptionLangmuirNoteApplicationIsotherm equationName
13. Adsorption isobar Graph between the amount adsorbed(x/m) and temperature at a constant equilibrium pressure of adsorbate gas is known as adsorption isobarChemisorption isobar shows an initial increase with temperature andthen expected decrease .The initial increase is because of the fact that the heat supplied acts as activation energy required in chemisorption.
14. Application of AdsorptionIn clarification of sugarIn gas masksIn catalysisIn adsorption indicatorsIn chromatographic analysisIn softening of hard waterIn preserving vacuumIn paint industryIn removing moisture from air in the storage of delicate instruments
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16. DIFFERENT PHYSICAL FORMS OF ACTIVATED CARBON
17. Need to make chemicals fasterMost Reactions are too slow to be useful...
18. Role of a CatalystCatalysts speed up a chemical reaction without being used up...Catalyst + ReactantsCatalyst-ReactantsCatalyst + Products
19. CatalysisPositive catalysisNegative catalysisAuto catalysis
20. Ways to Make Chemicals FasterPressureDisadvantage--Cause ExplosionsCatalysts!!!!Disadvantage--CostlyDisadvantage--Too hot!TemperatureAdd other ChemicalsDisadvantage--Separate chemicals
21. Thank you