Adsorption

The Freundlich adsorption isotherm is a scientific formula that helps describe how solutes interact with surfaces. It is typically written as:

where:

• is the amount of adsorbate per unit mass of adsorbent.
• is the concentration of the solute in the solution.
• and are constants.
  
  

To align with experimental data, we often convert this into a logarithmic form:

In this equation, is the intercept and is the slope of the line obtained in a plot of versus . In the options given, the correct answer relates to this slope.

The correct answer is:

• with to

This is because the slope in the logarithmic form of the Freundlich isotherm is exactly , and typically ranges between 0 and 1. This reflects the effectiveness of adsorption — if , it means that adsorption is favorable across a wide range of concentrations.

The correct answer is 12
Given that log K = intercept = 0.602 = log 4
∴ K = 4
Slope and
initial pressure = 0.03 atm

= 4 × 0.03 = 0.12 = 12 × 10^–2
∴ mass of gas absorbed per gm of adsorbent = 12 × 10^–2 g

Step 1: Recall the Freundlich Adsorption Isotherm}
The Freundlich adsorption isotherm is given by:

where is the mass of adsorbate, is the mass of adsorbent, is the pressure, is the Freundlich constant, and is a constant.
Step 2: Linearize the Equation
Taking the logarithm of both sides, we get:

This equation represents a straight line with slope and y-intercept .
Step 3: Compare with the Given Equation
The given equation is:

where and . Comparing this with the linearized Freundlich equation, we have:

Conclusion
The value of is , and is

The process involves three steps as indicated:
: Isobaric process
: Isochoric process
: Isothermal process
The total work done is given by:

For each step:



Substitute the values:


Using :



Convert to joules ( ):

• Physisorption:
– It decreases with an increase in temperature because it is an exothermic process (Statement C is correct).
– It requires no significant activation energy (Statement E is correct).
• Statements A, B, and D describe chemisorption and are incorrect for physisorption.
Thus, 2 statements (C and E) are correct.

A: Water vapours are adsorbed by calcium chloride. Calcium chloride (CaCl ) is a hygroscopic substance, meaning it has the ability to adsorb water vapors from the air. The water molecules are attracted to the surface of the calcium chloride, where they adhere through adsorption.

C: As the adsorption proceeds, becomes less and less negative. In the case of adsorption, the enthalpy change ( ) is initially negative because the process releases energy due to the attractive forces between the adsorbate and the adsorbent. However, as more water is adsorbed, the adsorption sites become occupied, and the heat released decreases, making less negative.