Question

Gaseous adsorption on solid surfaces is exothermic because adsorption brings in:
Options are-
(A) increase in enthalpy
(B) increase in entropy
(C) increases in free energy
(D) interaction forces developed between gaseous molecule and solid surface

Answer 1

An attempt to this question can be made by understanding the process of adsorption. Now define thermodynamic factors pertaining to the process of adsorption. Based on this you can determine the change in factors and thus choose the correct options.

Complete answer:
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface called the adsorbent. This process creates a film of the adsorbate on the surface of the adsorbent.
Similar to surface tension, adsorption is also a consequence of surface energy. In a bulk material, all the bonding requirements of the atoms of the material are filled by adjacent atoms in the material.
However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and thereby attract the adsorbate particles.
Gaseous adsorption on a solid surface is considered to be exothermic because adsorption brings in interaction forces developed between gaseous molecules and solid surfaces.
Along with that heat energy is always released in the process of gaseous adsorption.
Based on the above statements we can conclude that gaseous adsorption on solid surfaces is exothermic because adsorption brings in interaction forces developed between gaseous molecules and solid surfaces.

Therefore, the correct answer is option (D).

Note:
Adsorption and absorption are mistakenly considered to be the same process. However, absorption is a bulk phenomenon and occurs in the bulk of the material. On the other hand, adsorption is a surface phenomenon and occurs only on the surface the adsorbent substance. The process in which adsorption and absorption takes place together is called sorption.