Surface Chemistry Class 12- CBSE Chapter 5
The study of phenomena that occur on substance surfaces is referred to as surface chemistry. This is incredibly relevant to both the workplace and daily life. In other words, all surface phenomena are covered by surface chemistry.
What is Surface Chemistry?
It is the study of the chemical processes that take place when two surfaces—which may be solid-liquid, solid-gas, solid-vacuum, liquid-gas, etc.—come into contact. Surface engineering is a term used to describe some surface chemistry applications. On the surface of substances, a variety of phenomena can be seen, some of which include:
- Heterogeneous Catalysis
Applications of Surface Chemistry
Surface chemistry, when viewed broadly, is the study of how the surfaces of two different systems interact. This theory underlies some phenomena, such as:
- Colloid Formation
- Electrode Reactions
Major roles for surface chemistry are played in a number of chemical processes, including:
- Enzymatic reactions at the membranes and cell walls that make up biological interfaces.
- They are utilized in the electronics sector on the surface and interface of the computer microchips.
- The heterogeneous catalysts in the catalytic converter remove emissions in vehicle exhaust.
Role of Adsorption in Surface Chemistry
Adsorption is the process by which species at higher concentrations gather on a substance’s surface as a result of intermolecular forces. For instance, activated charcoal may absorb gases like H2, O2, and N2.
Enthalpy of Adsorption (EA): EA is the quantity of heat energy released when one mole of gas is adsorbed on the unit surface area of an adsorbent.
Types of Adsorption
Physical Adsorption or Physisorption
Between adsorbent and adsorbate, a weak van der Waals force is present.
- Van der Waals forces that are weak in nature
- Specificity: Its nature is not particular.
- Reversibility: The operation can be undone.
- Layer: The procedure has several layers.
- Adsorption enthalpy is low (between 20 and 40 KJ/mole).
- very little activation energy
- Desorption: Simple
- Adsorbent surface area, adsorbate type, pressure, and temperature are influencing variables.
Chemical Adsorption or Chemisorption
Strong chemical forces between the adsorbent and adsorbate are to blame.
- Strong chemical forces are the nature of forces.
- Specificity: extremely particular nature
- Reversibility: It cannot be undone.
- One layer makes up the procedure.
- Adsorption enthalpy: High adsorption enthalpy [40–400 KJ/mole]
- Extremely high activation energy
- Desorption: Very challenging
- Adsorbent surface area and adsorbate type, as well as temperature, are influencing factors.
Adsorbate and Adsorbent
A substance that is adsorbed on any surface is referred to as an adsorbate. For instance, gas is referred to be the adsorbate if it is adsorbed on the surface of a solid.
The substance on whose surface adsorption takes place is known as the adsorbent. The adsorbent could be liquid or solid. Frequently used adsorbents include metal powders, powdered charcoal, animal charcoal, silica powder, and others.
The act of desorption involves removing an adsorbate from a surface. The pressure in the system can be raised or lowered to achieve this.
When a substance’s molecules are uniformly distributed throughout the body of a solid or liquid, the phenomenon of absorption takes place.
Adsorption and absorption take place simultaneously during the phenomenon known as sorption. Just like other fibers, cotton absorbs dyes effectively.
While absorption takes time, adsorption happens quickly and instantly.
Factors affecting adsorption of gases on solids:
Nature of adsorbate: Physical adsorption is non-specific by nature, hence every gas will adsorb to some degree on the surface of any material. While H2, O2, N2, and other easily liquefiable gases are adsorbed to a smaller amount, gases with higher critical temperatures like NH3, HCl, and CO2 are absorbed to a greater extent. Due to the extreme specificity of chemical adsorption, gas will only bind to a particular material by chemical combination.
Nature of adsorbent: The most often utilized adsorbents include activated carbon, and metal oxides including aluminum oxide, silica gel, and clay. They have unique adsorption characteristics based on holes.
Specific area of the adsorbent: The extent of adsorption will be greater the larger the particular area. Because of this, more adsorbate can be absorbed by adsorbents that are porous or finely split. The pores ought to have enough room for the gas molecules to pass through.
The pressure of the gas: Pressure increase causes an increase in physical adsorption.
Adsorption isotherm: The word “adsorption isotherm” refers to the fluctuation in the amount of gas absorbed by the adsorbent with pressure at a constant temperature that can be described by a curve.
Freundlich Adsorption isotherm: At constant temperature, the connection between the gas’s pressure and x/m is known as the adsorption isotherm and is given by
Where, at a given temperature k and n, the nature of the gas determines the mass of the gas adsorbed on the mass m of the adsorbent, and the gas
Surface Chemistry Adsorption Isotherms
Freundlich Adsorption Isotherm
x/m = K [P^(1/n)]
‘x’ is the mass of adsorbate on the mass of adsorbent
⇒ log K/m = 1/n (log P + log K)
It does not apply to the adsorption of gases on solids at a higher pressure
Langmuir Adsorption Isotherm
One molecule thick layer of gas has been adsorbed on the solid adsorbent.
The homogenous adsorbed layer covers the entire adsorbent.
Adsorbed molecules next to one another do not interact.
Emulsions in Surface Chemistry
Emulsions are colloidal solutions in which the dispersed phase and the dispersion medium are both liquids.
Paints, colours, milk, and vanishing cream, for instance. Surface chemistry divides emulsions into two categories based on the dispersion medium:
Oil in Water Emulsions
This involves dispersing oil or fat droplets in water. Consider milk.
Water in Oil Emulsions
The water droplets in this are mixed with the oil. For instance, vanishing cream.
Emulsions are prone to instability, hence emulsifiers are typically added to improve stability. Example: Casein is a natural emulsion found in milk.
Applications of Emulsions
- These are used in syrups
- Digestion of fats
- Pigment and dye
Every significant formula and idea presented in the chapter is covered in the revision notes. Quick revision notes for surface chemistry class 12 are available to you if you need an overview of a chapter. These notes will undoubtedly save you time on those hectic exam days.