--%>
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 : Problem associated to vapour pressure

    Provide solution of this question. 60 gm of Urea (Mol. wt 60) was dissolved in 9.9 moles, of water. If the vapour pressure of pure water is P0 , the vapour pressure of solution is:(a) 0.10P0 (b) 1.10P0 (c) 0.90P0 (d) 0.99P0

    		•
  • Q : HCl is polar or non-polar Can you

    Can you please illustrate that HCl is polar or non-polar? Briefly illustrate it.

    		•
  • Q : Strength of Nacl in solution To 5.85gm

    To 5.85gm of Nacl one kg of water is added to prepare of solution. What is the strength of Nacl in this solution (mol. wt. of nacl = 58.5)? (a) 0.1 Normal (b) 0.1 Molal (c) 0.1 Molar (d) 0.1 FormalAnswer:

    		•
  • Q : Reason for medications contain hcl What

    What is the reason behind this that some medications contain hcl?

    		•
  • Q : Problem based on molarity Select the

    Select the right answer of the question. If 18 gm of glucose (C6H12O6) is present in 1000 gm of an aqueous solution of glucose, it is said to be: (a)1 molal (b)1.1 molal (c)0.5 molal (d)0.1 molal

    		•
  • Q : Explain preparation and properties of

    It may be prepared by the action of phosphorus on thionyl chloride.P4 + 8SOCl2    4

    		•
  • Q : The Liver Is Responsible For Much Of

    The Liver Is Responsible For Much Of The Pentose Phosphate Activity Explain

    		•
  • Q : How to calculate solutions molar

    The contribution of an electrolyte, or an ion electrolyte, is reported as the molar of a conductance. The definition of the molar conductance is based on the following conductivity cell in which the electrodes are 1 m apart and of sufficient area that th

    		•
  • Q : Question associated to vapour pressure

    Choose the right answer from following. The vapour pressure lowering caused by the addition of 100 g of sucrose(molecular mass = 342) to 1000 g of water if the vapour pressure of pure water at 25degree C is 23.8 mm Hg: (a)1.25 mm Hg (b) 0.125 mm Hg (c) 1.15 mm H

    		•
  • Q : Particles of quartz Particles of quartz

    Particles of quartz are packed by:(i) Electrical attraction forces  (ii) Vander Waal's forces  (iii) Covalent bond forces  (iv) Strong electrostatic force of attraction Answer: (iii)

    		•