Question

A particular adsorption process has the following characteristics: $1.$ it arises due to van der Waal forces $2.$ it is reversible. Identify the correct statement which describes the above adsorption process.
1. Adsorption in monolayer
2. Energy of activation is low
3. Adsorption increases with increase in temperature
4. Enthalpy of adsorption is greater than $100kJ\,mo{l^{ - 1}}$

Answer 1

In this the options given include many metal hydroxides. Almost all hydroxide ions form tight hydrogen bonds with water molecules in aqueous solutions with certain exceptions. As we have to find out the exothermic reaction here, we have to analyse the reaction in which heat is released and the energy is reduced.

Complete step by step answer:
There are two types of adsorption process, Physical adsorption process and chemical adsorption process.
Chemical Adsorption also known as Chemisorption takes place by chemical reaction taking place and it is a monolayer process since after the first layer undergoes adsorption through chemical process there is no further way of the second layer undergoing adsorption since molecules are left attached at the first level. The energy of activation will be quite high since a chemical change needs to take place.

Physical Adsorption is also known as physisorption takes place due to van der Waal force of attraction between the adsorbent (material on which adsorption takes place) and adsorbate (material getting adsorbed). According to the BET theorem, Physical adsorption can be multilayer since adsorbate molecules can get absorbed from the first layer and then through diffusion, get adsorbed on the second layer. Since this reaction is continuous and takes place spontaneously, the activation energy has to be low for the reaction to take place.

So, Option 2 is correct.

Note: Rate of Physisorption increases with decrease in temperature, and hence if a spontaneous reaction takes place at temperature closer to room temperature, it needs to have a small activation energy, which doesn’t require molecules to be given extra energy by temperature.