Types of Adsorption Isotherms Video Lecture | Physical Chemistry

Ans. There are several types of adsorption isotherms, including: - Langmuir isotherm: This isotherm assumes that adsorption occurs on a homogeneous surface with a limited number of identical sites available for adsorption. - Freundlich isotherm: This isotherm considers adsorption on a heterogeneous surface with a range of different adsorption sites, and the adsorption capacity decreases with increasing concentration. - BET isotherm: This isotherm is commonly used for multilayer adsorption and assumes that adsorption occurs in monolayers, with each layer having a different adsorption energy. - Temkin isotherm: This isotherm takes into account the interaction between the adsorbate and the adsorbent, assuming a linear decrease in adsorption energy with increasing coverage. - Dubinin-Radushkevich isotherm: This isotherm is used for microporous solids and considers the adsorption occurring through a three-dimensional network of pores.

Ans. The Langmuir isotherm is a model that describes the adsorption of a gas or solute onto a solid surface. It assumes that adsorption occurs on a homogeneous surface with a limited number of identical adsorption sites. According to this isotherm, the rate of adsorption is proportional to the concentration of the adsorbate in the gas or liquid phase. At equilibrium, the rate of desorption is equal to the rate of adsorption, resulting in a constant surface coverage. The Langmuir isotherm equation can be expressed as: 𝐶/𝑞 = 1/(𝑞𝑚𝑎𝑥 𝐾) + 𝐶/𝑞𝑚𝑎𝑥 Where C is the equilibrium concentration of the adsorbate, q is the amount of adsorbate adsorbed per unit mass of the adsorbent, qmax is the maximum adsorption capacity, and K is the adsorption equilibrium constant.

Ans. The Freundlich isotherm differs from the Langmuir isotherm in several ways. While the Langmuir isotherm assumes adsorption on a homogeneous surface with a limited number of identical adsorption sites, the Freundlich isotherm considers adsorption on a heterogeneous surface with a range of different adsorption sites. Additionally, the Freundlich isotherm does not assume a maximum adsorption capacity like the Langmuir isotherm. Instead, it describes the adsorption capacity as a function of the concentration of the adsorbate, with the adsorption capacity decreasing with increasing concentration. The Freundlich isotherm equation can be expressed as: 𝑞 = 𝐾𝐹𝐶^(1/𝑛) Where q is the amount of adsorbate adsorbed per unit mass of the adsorbent, C is the equilibrium concentration of the adsorbate, KF is the Freundlich constant related to the adsorption capacity, and n is the Freundlich constant related to the adsorption intensity.

Ans. The BET (Brunauer-Emmett-Teller) isotherm is commonly used for multilayer adsorption, particularly for the adsorption of gases onto solid surfaces. It assumes that adsorption occurs in monolayers, with each layer having a different adsorption energy. The BET isotherm is useful for determining the specific surface area of a solid material by analyzing the adsorption isotherm data. By plotting the quantity of adsorbed gas versus the relative pressure, a characteristic curve is obtained. The BET isotherm equation can be expressed as: 𝑝(𝑝0/𝑣)(1−𝑝/𝑝0) = 𝐶(𝑣−𝑣𝑚)/𝑣𝑚 Where p is the equilibrium pressure of the gas, p0 is the saturation pressure of the gas, v is the volume of the gas adsorbed, C is a constant related to the adsorption energy, and vm is the volume of the monolayer.

Ans. The Temkin isotherm is a model that takes into account the interaction between the adsorbate and the adsorbent. It assumes a linear decrease in adsorption energy with increasing coverage. According to this isotherm, the heat of adsorption of the molecules on the surface decreases linearly with the degree of coverage. The Temkin isotherm equation can be expressed as: 𝑞 = 𝐵ln(𝐴𝑠) + 𝐵ln(𝐶) Where q is the amount of adsorbate adsorbed per unit mass of the adsorbent, B is a constant related to the heat of adsorption, As is the equilibrium constant, and C is the constant related to the adsorption capacity.