Question

According to Freundlich adsorption isotherm, which of the following is correct?

• A. \(\dfrac{x}{m} \propto P^{0}\)
• B. \(\dfrac{x}{m} \propto P^{1}\)
• C. \(\dfrac{x}{m} \propto P^{\tfrac{1}{n}}\)
• D. All of these are correct for different ranges of pressure

Hint:

Freundlich adsorption isotherm explains adsorption only over a limited range of pressure:
Low pressure: linear relation
Intermediate pressure: fractional power law
High pressure: saturation

Answer 1

The Correct Option is D

Step 1: Freundlich adsorption isotherm is given by: \[ \frac{x}{m} = k P^{\frac{1}{n}} \] where \(k\) and \(n\) are constants and \(0<\frac{1}{n}<1\).
Step 2: At low pressure, adsorption is directly proportional to pressure: \[ \frac{x}{m} \propto P \] This corresponds to option (B).
Step 3: At moderate pressure, adsorption follows: \[ \frac{x}{m} \propto P^{\tfrac{1}{n}} \] This corresponds to option (C).
Step 4: At high pressure, the surface becomes saturated and adsorption becomes independent of pressure: \[ \frac{x}{m} \propto P^{0} \] This corresponds to option (A).
Step 5: Hence, all the given relations are valid but in different pressure ranges.