Question

Of physisorption or chemisorption, which has a greater enthalpy of adsorption?

Answer 1

Chemisorption and physisorption are the two types of adsorption. Adsorption is basically the accumulation of molecular species on the liquid and solid surfaces.

Step by step answer: First, we should know about adsorption. Adsorption is the surface phenomena in which the molecules get adsorbed on the surface of the solid or liquid. The solvent that adsorbed is called adsorbate and the surface on which the solvent gets adsorbed is called adsorbent.
Types of adsorption:
Physisorption: It involves the physical changes where Van Der Waals forces of attraction take place. It is reversible and not specific in nature. Physisorption is inversely proportional to the temperature which means as temperature increases physisorption decreases. Vander Waal forces are very weak that’s why it results in the multimolecular layer. Activation energy is very less. Enthalpy of adsorption is very low about 20 to 40 kJ per mole.
Chemisorption: Chemical changes take place because chemical bonding involves in the chemisorption. Chemical bond is stronger than Van Der Waal forces that’s unimolecular layer forms in chemisorption. It has higher enthalpy of adsorption i.e., 80 to 240 kJ per mole. Activation energy is high and as temperature increases the rate of chemisorption also increases.
Thus, chemisorption has greater enthalpy of adsorption i.e., 80 to 240 kJ per mole.

Note: Remember that, chemisorption and physisorption both are surface phenomena and exothermic in nature. There are many similarities between them like as surface area increases then both phenomena increases.