--%>
Assignment Help - homework help

Describe physical adsorption and its characteristics.

When the forces of attraction existing between adsorbate and adsorbent are van der Waal's forces, the adsorption is called physical adsorption. This type of adsorption is also known as physisorption or van der Waal's adsorption. Since the forces existing between adsorbent and adsorbate are very weak, therefore, this type of adsorption can be easily reversed by heating or by decreasing the pressure.

Characteristics of Physisorption

Some of the important characteristics of physisorption are as follows:

(i) Deficient of specificity: since the van der Waal forces are universal, a given surface of adsorbent does not show any preference for any specific gas. It can adsorb all the gases but to a different extent.

(ii) Reversible nature: physical adsorption of a gas by the solid is reversible and thus equilibrium is reached rapidly

Solid + Gas  1387_Physical adsorption.png  gas/solid + Heat

Thus, according to Le-chatelier's principle,

(a) Increase of pressure pushes the equilibrium in forward direction leading to more adsorption of gas and decrease of pressure cause desorption to occur.

(b) Since process is exothermic, therefore, lowering of temperature favours more adsorption and increase of temperature leads to desorption.

(iii) Surface area of adsorbent: the extent of adsorption increase with the increase of surface area of adsorbent. Thus, finely divided metals and rough surfaces are good adsorbents.

(iv) Nature of adsorbate: the amount of gas adsorbed by solid depends on nature of gas. In general, easily liquefiable gases (i.e gases with higher critical temperature) are readily as van der Waal forces are stronger near the critical temperature.

(v) Enthalpy of adsorption: the enthalpy of adsorption is low (20-40 kJ mol-1). This is because of weak nature of van der Waal's forces.

(vi) State of adsorbate: molecular state of adsorbate remains unaltered.

(vii) Activation energy: physical adsorption does not involve any chemical reaction and therefore, it requires very low activation energy.

   Related Questions in Chemistry

  • Q : Molarity what is the molarity of the

    what is the molarity of the solution prepared by dissolving 75.5 g of pure KOH in 540 ml of solution

    		•
  • Q : Kinds of insulators Describe all the

    Describe all the kinds of insulators which are present?

    		•
  • Q : What is heat capacity and how to

    The temperature reliance of internal energy and enthalpy depends on the heat capacities at constant volume and constant pressure. The internal energy and enthalpy of chemical systems and the energy changes that accompany chemical reactions depend on the

    		•
  • Q : Application of colligative properties

    Choose the right answer from following. Colligative properties are used for the determination of: (a) Molar Mass (b) Equivalent weight (c) Arrangement of molecules (d) Melting point and boiling point (d) Both (a) and (b)  

    		•
  • Q : Finding Normality Can someone please

    Can someone please help me in getting through this problem. Concentrated H2SO4 has a density of 1.98 gm/ml and is 98% H2SO4 by weight. The normality is: (a) 2 N  (b) 19.8 N  (c) 39.6 N  (d) 98

    		•
  • Q : Explain Photoelectron Spectroscopy. The

    The energies of both the outer and inner orbitals of atoms and molecules can be determined by photoelectron spectroscopy.Energy changes of the outermost or highest energy electron of molecules were dealt with here in a different passion. The energies of ot

    		•
  • Q : Concentration of Sodium chloride

    Provide solution of this question. If 25 ml of 0.25 M NaCl solution is diluted with water to a volume of 500ml the new concentration of the solution is : (a) 0.167 M (b) 0.0125 M (c) 0.833 M (d) 0.0167 M

    		•
  • Q : Which is largest planet in our solar

    which is largest planet in our solar system

    		•
  • Q : What are aliphatic amines and its

    In common system, the aliphatic amines are named by using prefix for alkyl group followed by the word amine.In case of mixed amines, the name of alkyl groups are arranged in alphabetical order. This is followed by the word amine. However, for simple secondary or tertiary amines anothe

    		•
  • Q : Problem on molarity-normality-molality

    Can someone please help me in getting through this problem. The solution ofAl2(SO4)3 d = 1.253gm/m comprise 22% salt by weight. The molarity, normality and molality of the solution is: (1) 0.805 M, 4.83 N, 0.825 M (2)

    		•