Understanding Physical Adsorption Isotherms
Physical adsorption, also known as physisorption, involves the weak van der Waals forces between adsorbate molecules and adsorbent surfaces. The isotherm models describe how these molecules interact with the surface at varying pressures and temperatures.
Isotherm Types:
- Langmuir Isotherm: This model assumes monolayer adsorption on a surface with a finite number of identical sites. It is more applicable to chemisorption than physisorption.
- BET Isotherm: The Brunauer-Emmett-Teller (BET) model extends the Langmuir theory to multilayer adsorption. It is primarily used for physical adsorption but is more complex than necessary for simple cases.
- Freundlich Isotherm: This is an empirical model that describes adsorption on heterogeneous surfaces. It is applicable to physical adsorption as it accounts for diverse adsorption sites and interactions among adsorbate molecules.
- Kisluik Isotherm: This is less commonly used and is not specifically tailored for either physisorption or chemisorption.
Why Freundlich is Correct:
- Heterogeneous Surfaces: The Freundlich isotherm accommodates the varied energy of adsorption sites, typical in physical adsorption scenarios.
- Empirical Nature: Its empirical approach allows it to fit experimental data without strict assumptions about the adsorbent surface.
- Multilayer Formation: It can represent multilayer adsorption, a common phenomenon in physical adsorption processes.
Conclusion:
Given these characteristics, the Freundlich isotherm is indeed the most suitable model for describing physical adsorption processes among the options provided.