Question

Reversible adsorption is:
(A)Chemical adsorption
(B)Physical adsorption
(C)Both
(D)None

Answer 1

Hint:Adsorption is a surface phenomenon. It is the process of accumulation of species at the surface rather than in the liquid or solid. There are two kinds of adsorption that takes place when gas is adsorbed on a solid surface. It is a surface phenomenon.

Complete answer:We know that there are two types of adsorption of gases on solids. One is physisorption and another one is chemisorption. If the gas accumulation on the surface of solid takes place due to weak van der waal forces then it is termed as physisorption or physical adsorption. Here in physisorption the amount of adsorption decreases with increase of temperature and increases with increase of pressure. It is a reversible process.
Now if the gas molecules are held to the surface by chemical bonds , then this adsorption is known as chemical adsorption or chemisorption. The chemical bonds may be ionic or covalent. This process needs a higher activation energy and is commonly referred to as activated adsorption.So the reversible adsorption here is physisorption and the irreversible adsorption is chemisorption.

Additional Information:Physical adsorption is inversely proportional to temperature since physical adsorption is an exothermic process .

Hence the correct answer is option (B).

Note:Chemisorption happens due to some specific types of forces so it is irreversible. Also lack of specificity, surface area of adsorbent, enthalpy of adsorption are important characteristics of physical adsorption. Similarly high specificity, surface area of adsorbent and enthalpy of adsorption are important properties of chemical adsorption.