Explain the following observations. a. Sun looks red at the time of sunset. b. Rate of physical adsorption decreases with rise in temperature. c. Physical adsorption is monolayered.
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At the time of sunset, the sun is at horizontal. The light emitted by the sun has to travel a relatively longer distance through the atmosphere. As a result, blue part of light is scattered away by the particulate in the atmosphere causing red part to be visible. b. Gas (adsorbate)+Solid (adsorbent) `overset("Condensation")underset("Evaporation")hArr` Gas adsorbed on solid + Heat Physical adsoption in an exothermic process. At equilibrium as temperature is increased, by Le-Chaterlier's principle, the equilibrium shifts in the backward direction, i.e., adsorption decreases. c. Physical adsorption involves van der Waals forces, so any number of layers may be formed one over the other on the surface of the adsorbent. Chemical adsorption takes place as a result of the reaction between adsorbent and adsorption adsorbate. When the surface of adsorbent is covered with one layer, no further reaction can take place.
