Introduction

Surface chemistry is a branch of physical chemistry that deals with the study of phenomena that occur at the interface. The following article is all about such phenomena that is adsorption vs absorption and their reactions.

In daily life, various chemical reactions occur on the surface of the solids like corrosion occurs as the metal reaction takes place on the surface. The free surfaces of any phase are known as the interface. The plane where the two stages meet is called the interface. There is no interface between the gases.

Therefore they form confusing and homogeneous solutions. Because a lot of phenomena occur in interfaces such as heterogeneous, catalysis, electrode process, corrosion, etc. Hence, all of these phenomena are discussed in surface chemistry. One such phenomenon is sorption. Sorption is a physical and chemical process where the molecules of matter are connected to each other. Absorption and adsorption are two parts of this sorption (2) & (3).

Adsorption

It is the occurrence of a substance accumulating or concentrating on the surface of a substance without entering another substance in contact with it. Adsorption of the soluble solution of gas or any solution usually occurs on the surface of solids. On the other hand, gas is adsorbed on the surface of a liquid. Substances that adsorb other substances on the surface are called adsorbents. Such as activated charcoal, silica gel, bentonite, etc. The substances that get adsorbed on the surface are called adsorbate example gases such as ammonia, hydrogen, carbon dioxide, oxygen, etc. are adsorbed by activated charcoal (1) & (4).

Example of adsorption (1)

• Acetic acid and iodine are adsorbed by charcoal.
• Nitrogen gas is adsorbed on mica.
• Oxygen gas is adsorbed on the tungsten surface.
• Water vapor is adsorbed by silica gel.

Causes of adsorption

The cause of adsorption is the unequal force acting on the surface particles of the adsorbent. Adsorption is a completely superficial phenomenon that occurs on the surface of solids or liquids.

The energetic state of the particles is different from that of a particle inside the adsorbent. It is surrounded by similar particles all around it and the force of gravity acting on the quadrilateral is zero. However since the particle on the surface of the adsorbent does not have a neighboring particle on one side, it is under an asymmetric ball. Therefore, the free energy of the particles is also higher. Particles on the surface of the adsorbent adsorb molecules, atoms, or ions of other substances in order to reduce free energy (2) & (3).

Types of adsorption

Adsorption is of two types namely physical adsorption and chemical adsorption.

1. Physical adsorption

The process of adsorption in which the particles of the adsorbed material are attached to the surface of the adsorbent by the weak van der Waals force of attraction is called physical adsorption (3).

Characteristics

1. Physical adsorption tends to be parabolic in nature.
2. As the pressure increases, the rate of physical adsorption increases.
3. This type of adsorption rate decreases as the temperature increases.
4. The amount of heat generated by such adsorption is very low.
5. If the surface area and porosity of the adsorbent increase, the level of physical adsorption also increases.
6. In physical adsorption, the gaseous layer molecules formed on the surface of the solid adsorbent can bind other gaseous molecules on them through the van der Waals force. In this case, a multimolecular layer of molecules of the adsorbed gas substance is formed on the surface of the adsorbent.

2. Chemical adsorption

The process of adsorption in which the particles of the adsorbed substance are bound to the surface of the adsorbent by chemical bonding is called chemical adsorption.

Characteristics

1. Chemical adsorption is irreversible in nature.
2. This type of adsorption rate increases when the pressure increases.
3. If the surface area and porosity of the adsorbent increase, the level of chemical adsorption also increases.
4. As the temperature increases, the rate of chemical adsorption increases. However, at very high temperatures, the rate of adsorption gradually decreases.
5. The amount of activation energy is higher in this type of adsorption.
6. In chemical adsorption, the particles of the adsorbed substance on the surface of the adsorbent are joined by chemical bonds. The range of the active force in this bond is very small. Therefore, the particles of the adsorbed substance are bound in a single molecular layer on the surface of the adsorbent.

Absorption

Absorption is an important term in surface chemistry. It is a physical or chemical process and is a different process from adsorption. Absorption is a process in which a substance is absorbed by a liquid or a solid. This process occurs when molecules enter a bulk phase. This process is not affected in any way by temperature. During the process of absorption, the molecules form a solution by dissolving the solvent completely. Once the molecules are dissolved, they cannot be easily separated from the absorbent (1) & (4).

Example of absorption

• Water vapor is absorbed by anhydrous calcium chloride.
• Ammonia is absorbed by water to form ammonium hydroxide.
• Water vapor is absorbed by phosphorous pentoxide (4).

Types of absorption

There are two types of absorption, physical absorption, and chemical absorption (3) & (4).

1. Physical absorption

It is a non-reactive process. This process depends on physical properties such as solubility, temperature, and pressure. Hydrophilic solids, which include many solids from biological sources, can easily absorb water.

2. Chemical absorption

Chemical absorption is a reactive process. It is a chemical reaction between the absorbent and the absorbed substance. This process occurs when the atoms or molecules are absorbed. When hydrogen sulfide is removed from natural gas and converted into solid Sulphur.

Uses of absorption

The uses of absorption are mainly in space cooling applications, cold storage, turbine inlet cooling, ice production, clean-burning fuels, high-efficiency operation, and a few moving parts, etc. (4).

Adsorption vs Absorption

The word adsorption and adsorption are two important processes in chemistry. Absorption is a process by which molecules enter a bulk phase and are absorbed by a liquid or a solid. Adsorption is a process that occurs on the surface of solids. Absorption and adsorption take place. Both processes are the parts of sorption. But there are some differences between them that are discussed below (1) & (4).