4.1 Freundlich adsorption isotherm

2.1 Characteristics of Adsorption
2.2 Types of Adsorption

4.1 Freundlich adsorption isotherm
4.2 The Langmuir adsorption isotherm

7.1 Different Colloidal Systems
7.2 Classification of Colloidal System
7.3 Preparation of Colloidal System
7.4 Purification of Colloidal System
7.5 Properties of colloidal system

8.1 Protective colloids

9.1 Foams
9.2 Applications of colloids and emulsions

10.1 Positive and negative catalysis
10.2 Types of catalysis

12.1 Characteristics of Enzymes
12.2 Mechanism of enzyme catalysis
12.3 Autocatalysis
12.4 Induced catalysis

Freundlich gave an empirical relationship between the quantity of gas adsorbed by a given amount of solid adsorbent surface and pressure of the gas at a particular temperature. It states that $$\frac{x}{m} = k{p^{1/n}}$$

where $x$ is the weight of the gas adsorbed by $m$ gm of the adsorbent at a pressure $p$;

thus $x/m$ represents the amount of gas adsorbed per gm (unit mass) of the adsorbent,

$k$ and $n$ are constants at a particular temperature and for a particular adsorbent and adsorbate (gas) :

$n$ is always greater than one, indicating that the amount of the gas adsorbed does not increase as rapidly as the pressure.

When $n = 1$, $$\frac{x}{m} = kp$$ $$\frac{x}{m} \propto p$$

This is observed in lower pressure range. When $n$ is large, $\frac{x}{m} = k$ (independent of pressure). This is observed at high pressure when saturation point is reached as shown in figure $2$.

Taking logarithm of the equation $$\frac{x}{m} = k{p^{1/n}}$$

$$\log \frac{x}{m} = \log k + \frac{1}{n}\log p$$

Graph between $\left( {\log \frac{x}{m}} \right)$ and $\log p$ is a straight line with $slope\frac{1}{n}$ and intercept $\log k$ as shown in figure $3$.