Surface Chemistry

Physisorption is the process of adsorption where gas molecules are held on the surface of a solid by van der Waals forces. It is a physical process that does not involve any chemical bonding, and it occurs at low temperatures. The key characteristics of physisorption are:

- It arises due to van der Waals' forces (Option A).
- It is non-specific, meaning it is not dependent on the type of adsorbate (Option B).
- It depends on the nature of the gas, as gases with larger molecules or higher polarizability are more likely to adsorb (Option D).
- The enthalpy of adsorption is low (usually between 20 - 40 kJ mol ) (Option E).

However, physisorption does not require high activation energy (Option C). This is because the forces involved are weak, and the adsorption process is spontaneous at low temperatures without needing a significant energy barrier.

Thus, the incorrect statement is that high activation energy is needed for physisorption.

The correct option is (C) : High activation energy is needed

Adsorption isotherm analysis:

The Freundlich adsorption isotherm gives the empirical relationship:

Taking logarithms:

Comparison with options: This matches exactly with option (D).

Thus, the correct option is (D): .