Adsorption Isotherms Applications - Explain, FAQs

Adsorption Isotherm

The variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve termed as adsorption isotherm. Or in other words, the plots of extent of adsorption(x/m) vs pressure at constant temperature are called Adsorption isotherms.

Here 'x' refers to the mass of gas adsorbed by 'm' the mass of adsorbent.

Factors Affecting Adsorption Isotherm

The extent of adsorption increases with the increase of surface area per unit mass of the adsorbent at a given temperature and pressure.

Also read -

• NCERT Solutions for Class 11 Chemistry
• NCERT Solutions for Class 12 Chemistry
• NCERT Solutions for All Subjects

Adsorption Isotherms: Understanding and Implications

Adsorption isotherms are graphic representations of the interaction of adsorbate-adsorbent at constant temperature. It plots the amount of adsorbate on the adsorbent versus its fluid-phase concentration to project a view of the adsorption process. Keywords:

• Adsorbate: It means the adsorbed substance.
• Adsorbent: It refers to the material on which adsorption will take place.
• Isotherm: It is the curve showing the variation of adsorbate concentration under constant temperature with its adsorption extent.

The characteristic studies of adsorption isotherms would make it possible to understand the surface properties and capacities of different adsorbents so an effective adsorption system could be designed.

Types of Adsorption Isotherms

There are different types of adsorption isotherm models, all with their own characteristics. These include:

1. Langmuir Isotherm: Assumption of monolayer adsorption onto a surface comprising a finite number of adsorption sites. It is characterized by the equation:

The Langmuir adsorption isotherm equation is given by:

$$\theta=\frac{b P}{1+b P}$$

where:

$\theta$ is the fraction of the surface covered by the adsorbate

P is the pressure of the adsorbate.
? is the Langmuir constant

2. Freundlich Isotherm: Applied for heterogeneous surfaces, it can commonly be expressed as:

The Freundlich adsorption isotherm equation is given by:

$$
x / m=k P^{1 / n}
$$

where:
$x / m$ is the amount of adsorbate per unit mass of adsorbent.
$P$ is the pressure of the adsorbate.
$k$ and $n$ are empirical constants specific to the system.

3. BET Isotherm: Generalization of the Langmuir model for multilayer adsorption usually applied for porous materials.

Each model offers insights into different dimensions of the interaction of adsorbate with the surface, hence providing clues to choosing relevant models depending on the application.

Relevance and Applications

Adsorption isotherms find application in the following industrial and research sectors:

• Environmental Engineering: Adsorption isotherms turn out to be useful during water and air treatments in the selection and design of adsorbents for removing contaminants.
• Pharmaceuticals: The principles of adsorption are utilized in drug delivery systems by controlling the release of active ingredients.
• Chemical Engineering: Understanding adsorption isotherms helps in the design of catalysts and reactors.
• Agriculture: In soil science, adsorption isotherms are applied to the study of nutrient uptake and pesticide behavior.

The applicability of adsorption isotherms in academic research falls under very significant application. Characterization of novel materials and understanding their surface properties are fundamentally important in the materials field. They provide insights into the adsorption mechanisms critical in developing innovative solutions in the domain of science.

Also Read:

• NCERT solutions for Class 12 Chemistry Chapter 5 Surface Chemistry
• NCERT Exemplar Class 12 Chemistry Solutions Chapter 5 Surface Chemistry
• NCERT notes Class 12 Chemistry Chapter 5 Surface Chemistry

Recommended topic video on(adsorption isotherms)

Some Solved Examples

Question 1: The curve showing the variation of adsorption with pressure at constant temperature is called?

1) An innovative
2) Adsorption isotherm
3) Adsorption isobar
4) All are incorrect

Solution:
The correct answer is option (2), Adsorption isotherm. An adsorption isotherm represents the relationship between the amount of gas adsorbed by an adsorbent and the pressure of the gas at a constant temperature.

Question 2:

At the equilibrium position in the process of adsorption $\qquad$
1) $\Delta H>0$

2) (correct) $\Delta H=T \Delta S$

3) $\Delta H>T \Delta S$

4) $\Delta H<T \Delta S$

Solution: The answer is option (2).At equilibrium position during adsorption, $\Delta G=\Delta H-T \Delta S=0$ So that $\Delta H=T \Delta S$

Hence, the answer is option (2).

Question 3: For Freundlich adsorption isotherm, a plot of $\log \left(\frac{x}{m}\right)$ (y-axis) and $\log p$ ( $x$-axis) gives a straight line. The intercept and slope for the line are 0.4771 and 2 , respectively. The mass of gas, adsorbed per gram of adsorbent if the initial pressure is 0.04 atm , is $\times 10^{-4} g \cdot(\log 3=0.4771)$

Solution:

So, The mass of gas, adsorbed per gram of adsorbent means Need to find $\mathrm{x} / \mathrm{m}$ which is -

$
\begin{aligned}
& \frac{x}{m}=K P^{1 / n} \\
& \log \left(\frac{x}{m}\right)=\frac{1}{n} \log P+\log K \\
& \text { Slope }=\frac{1}{n}=2 \\
& \text { intercept }=\log K=0.4771 \\
& K=3
\end{aligned}
$

mass of gas adsorbed per gm of adsorbent $=\frac{x}{m}$

$
\frac{\mathrm{x}}{\mathrm{~m}}=3 \times(0.04)^2=48 \times 10^{-4}
$

Hence, the answer is (48)

Practice More Questions With The Link Given Below:

Summary

Adsorption isotherms are among the preferred methods of understanding substance–surface interactions. They guide practical applications in such wide fields as environmental engineering, pharmaceuticals, and even chemical engineering. Knowing the basics of adsorption isotherms, their types, and applications will help us achieve an all-rounded understanding of this key process. The adsorption isotherms can not only help design a viable adsorption system but also enhance our capabilities towards pollution control, advanced material development, and many more.

Also Read