Question

Give reason why a finely divided substance is more effective than as an adsorbent.

Answer 1

Try to recall that in heterogeneous catalysis metals like Ni, Pt etc. are used as catalysts but in a finely divided form to increase its surface area. Now, by using this you can easily answer the given question.

Complete step by step solution:
It is known to you that the extent of adsorption of a gas on a solid surface depends on many factors, of which one is specific area of the adsorbent.

• In heterogeneous catalysis, adsorption of reactants on solid surfaces takes place. The metals such as Fe, Ni, Pt, Pd, etc. are used in the manufacturing process and in finely divided form.
• The specific area of adsorbent is the surface area available for adsorption per gram of adsorbent.
• The larger the surface area of the solid, the greater would be its adsorbing capacity.
• Therefore, the porous and finely divided forms of adsorbents adsorb large quantities of adsorbate.
• However, the pores of adsorbent should be large enough to allow the gas molecules to enter them.
• In manufacturing of ammonia using finely divided iron as catalyst, manufacture of sulphuric acid by contact process and use of finely divided nickel in hydrogenation of oils are excellent examples of use of finely divided metals.

Note:

• It should be remembered to you that the adsorption also depends upon the nature of the gas adsorbed. Higher the critical temperature of gas to be adsorbed, more readily it will be adsorbed.
• Also, you should remember that the process of adsorption is an exothermic process and is invariable accompanied by evolution of heat.