--%>
Assignment Help - homework help

What is chemisorption or chemical adsorption?

When the forces of attraction existing between adsorbate particles and adsorbent almost of the same strength as chemical bonds, the adsorption is called chemical adsorption. This type of adsorption is also known as chemisorptions. Since forces of attraction existing between adsorbent and adsorbate are relatively strong, therefore, this type of adsorption cannot be easily reversed. 

Characteristics of chemisorptions

Some important characteristics of chemisorptions are as follows:

(i) High specificity: chemisorptions is highly specific in nature. It occurs only if there is a possibility of bond formation between adsorbent and adsorbate molecules. For example O2 is adsorbed on metals by virtue of oxide formation and H2 is absorbed by transition metals due to hydride formation.

(ii) Irreversibility: as chemisorptions involve the compound formation between adsorbent and adsorbate, it is generally irreversible.

(iii) Enthalpy of adsorption: attractive forces between adsorbent and adsorbate molecules are strong chemical bonds and therefore, molar heat of adsorption is high and is of the order of 200-400 kJ mol-1.

(iv) High activation energy: although chemisorptions is exothermic, yet the process is slow at low temperature. It is because of high activation energy required for chemical process to occur. Like most of the chemical changes the extent of chemisorption increases initially with rise in temperature. High pressure is also supporting for chemisorption.

(v) Surface area: like physisorption, chemisorption also increases with increase in surface area of adsorbent.

(vi) State of adsorbate: since chemical reaction takes place in this type of adsorption, therefore, the molecular state of adsorbate molecules may be altered. For example, oxygen exists as O2, but on the surface where it is chemisorbed, it may exist as O2-, O22-, O-, O, O3-, etc.

(vii) Activation energy: chemical adsorption involves a chemical reaction between adsorbent and adsorbate; therefore, it requires high activation energy.

The adsorption of N2 on iron under two different conditions provides distinction between physisorption and chemisorption. At 83 K nitrogen gas undergoes physical adsorption on iron surface. N2 molecules are amount of N2 adsorbed decreases with further rise in temperature. At room temperature there is almost again shows adsorption as N atoms on the iron surface. This mode of adsorption is chemical adsorption as atoms form chemical bonds with iron atoms.

   Related Questions in Chemistry

  • Q : Solution and colligative properties

    what is molarity of a solution of hcl which contains 49% by weight of solute and whose specific gravity is 1.41

    		•
  • Q : Define Virial Equation The constant of

    The constant of vander Waal's equation can be related to the coefficients of the virial equation.  Vander Waal's equation provides a good overall description of the real gas PVT behaviour. Now let us

    		•
  • Q : The Liver Is Responsible For Much Of

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

    		•
  • Q : Explain Ionic Bond with examples. The

    The bonding in ionic molecules can be described with a coulombic attractive term.For some diatomic molecules we take quite a different approach from that used in preceding sections to describe the bonding. Ionic bonds are interpreted in terms of the coulom

    		•
  • Q : Biodegradable polymers what are the

    what are the examples of biodegradable polymers

    		•
  • 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 : Problem related to molarity Provide

    Provide solution of this question. Increasing the temperature of an aqueous solution will cause: (a) Decrease in molality (b) Decrease in molarity (c) Decrease in mole fraction (d) Decrease in % w/w

    		•
  • Q : Molar mass of solute The boiling point

    The boiling point of benzene is 353.23 K. If 1.80 gm of a non-volatile solute was dissolved in 90 gm of benzene, the boiling point is increased to 354.11 K. Then the molar mass of the solute is: (a) 5.8g mol-1  (b)

    		•
  • Q : Symmetry Elements The symmetry of the

    The symmetry of the molecules can be described in terms of electrons of symmetry and the corresponding symmetry operations.Clearly some molecules, like H2O and CH4, are symmetric. Now w

    		•
  • Q : Net charge of a non-ionized atom

    Describe the net charge of a non-ionized atom?

    		•