Surface Chemistry



1   Write any two Characteristics of Chemisorption.

Solution :

(i) Chemisorption is highly specific in nature. If chemical bonds exist between adsorbate and adsorbent then the adsorption is chemical adsorption.$\\$ (ii) On increase in temperature initially the rate of reaction increases and on further increase in temperature desorption occurs.

2   Why does physisorption decrease with the increase of temperature?

Solution :

Physisorption is exothermic in nature. Therefore, in accordance with Le-Chateliere’s principle, it decreases with an increase in temperate. The means that physisorption occurs more readily at a lower temperature.

3   Why are powdered substances more effective adsorbents than their crystalline forms?

Solution :

Powdered substances are more effective adsorbents than their crystalline forms because when a substance is powdered, its surface area increases and physisorption is directly proportional to the surface area of the adsorbent.

4   Why is it necessary to remove $CO$ when ammonia is obtained by Haber’s process?

Solution :

It is important to remove $CO$ in the synthesis of ammonia as $CO$ adversely affects the activity of the iron catalyst, used in Haber’s process.

5   Why is the ester hydrolysis slow in the beginning and becomes faster after sometime?

Solution :

Ester hydrolysis can be represented as:$\\$ Ester + Water $\to$ Acid + Alcohol$\\$ The acid produced in the reaction acts as a catalyst and makes the reaction faster. Substances that act as catalysts in the same reaction in which they are obtained as products are know as auto catalysts.