Surface Chemistry

Surface chemistry is referred to as the study of the phenomenon occurring on the surfaces of substances. This is very applicable in industries and day to day lives. In other words, surface chemistry deals with all types of surface phenomenon.

Table of Content

• Applications of Surface Chemistry
• Role of Adsorption
• Types of Adsorption
• Effects of Pressure and Temperature
• Adsorption Isotherms
• Emulsions

What is Surface Chemistry?

It is the study of the chemical phenomena that occur at the interface of two surfaces which can be solid-liquid, solid-gas, solid-vacuum, liquid-gas, etc. Some applications of surface chemistry are known as surface engineering. There are various phenomena taking place on the surface of substances and some of them are:

• Adsorption
• Heterogeneous Catalysis
• Corrosion
• Crystallization

Applications of Surface Chemistry

In a wider perspective, surface chemistry deals with the interaction of surfaces of one system with that of the other system. Some phenomena work on this principle such as:

• Catalysis
• Colloid Formation
• Electrode Reactions
• Chromatography

Surface Chemistry has a major role in various chemical processes such as:

• Enzymatic reactions at the biological interfaces found in the cell walls and membranes.
• In the electronics industry, they are used in the surface and interface of microchips found in computers.
• In automobile exhausts, the heterogeneous catalysts found in the catalytic converter for cleaning emissions.

Role of Adsorption in Surface Chemistry

Accumulation of species on higher concentration on the surface of a substance due to intermolecular force is known as adsorption. For Example, gases such as H2, O2, N2 adsorbs on the surface of activated charcoal.

Enthalpy of Adsorption: The amount of heat energy liberated when one mole of gas is adsorbed on the unit surface area of adsorbent is known as enthalpy of adsorption.

Types of Adsorption

Due to the force of interaction between adsorbate and adsorbent, adsorption in surface chemistry is classified into two types.

Physical Adsorption or Physisorption

There exists a weak van der Waals force between adsorbate and adsorbent.

Characteristics:

• Nature of forces: weak van der Waals forces
• Specificity: It is not specific in nature
• Reversibility: The process is reversible
• Layer: It is a multi-layered process
• Enthalpy of adsorption: Low enthalpy of adsorption [ 20 – 40 KJ/mole ]
• The energy of activation: Very low
• Desorption: Very easy
• Factors affecting: Surface area of adsorbent nature of adsorbate, pressure, temperature.

Chemical Adsorption or Chemisorption

It is due to strong chemical forces between adsorbate and adsorbent.

Characteristics:

• Nature of forces: Strong chemical forces
• Specificity: Highly specific nature
• Reversibility: It is irreversible
• Layer: It is a single-layered process
• Enthalpy of adsorption: High enthalpy of adsorption [40 – 400 KJ/mole]
• The energy of activation: Very high
• Desorption: Very difficult
• Factors affecting: Surface area of adsorbent, nature of adsorbate Temperature.