Surface chemistry refers to the study of chemical reactions that happen on the interfaces or the surfaces of any material. The bulk of phases we encounter in surface chemistry could be pure compounds or solutions. Solid-gas or solid/gas can be used to represent the interface between a solid and a gas. For example, due to absolute miscibility, there is no interaction between the two gases.
Surface chemistry in NCERT class 12 has many applications in industry, research, and daily life. Rusting, electrode processes, dissolution, heterogeneous catalysis, and crystallisation are all examples of significant phenomena that occur at interfaces.
To conduct precise surface tests, it is essential to have an immaculate surface. Solid residues with such pristine surfaces must be stored in a vacuum, or the molecules of the primary components of air, dioxygen, and dinitrogen, will cover them. Now it is possible to get super clean metal surfaces at a high vacuum, on the scale of 10 to 10 pascal. In this unit, you will learn about adsorption, catalysis, and colloids such as emulsions and gels.
1. Adsorption is the process of a solid (or a liquid) attracting and keeping the molecules of a substance on its surface, resulting in a more significant concentration of the molecules on the surface or an interface.
2. The adsorbate is the adsorbent component, while the adsorbent is the substance that adsorbs.
3. Desorption is removing an adsorbed material from the surface it is adsorbed on.
4. Absorption is not the same as adsorption. The material is equally absorbed through the surface of a liquid, interface, or a solid during the process of absorption.
5. Physical adsorption or physisorption is a process in which the adsorbate is retained by weak van der Waals forces on the surface. Heating or lowering the pressure can reverse this form of adsorption.
6. Chemisorption or chemical adsorption occurs whenever the forces keeping the adsorbate to the surface are comparable to chemical bond forces. This form of adsorption cannot be reversed.
7. Adsorption is usually accompanied by heat release, making it an exothermic reaction.
8. The following factors determine the extent of a gas's adsorption on a solid: the nature of the adsorbate; the adsorbent; the temperature; and the pressure.
9. An adsorption isotherm is a relationship or chart between both the amplitude of adsorption( x/m) and the pressure (P) of a fixed amount of gas temperature.
10. Isotherm of Freundlich adsorption: A line is drawn with a (In) slope plotted between log x/m and log P. It keeps well at room temperature; n = 1 at low pressure.
11. The following assumptions underpin the Langmuir adsorption isotherm:
(I) Each adsorption region is identical in every way.
(ii) A particle's ability to bind at a specific site is unaffected by whether or not neighboring sites are occupied.
12. A catalyst is a substance that can affect the reaction rate while remaining chemically unchanged at the end.
5.1. Write any two characteristics of Chemisorption.
Ans: Pt and Pd are inert electrodes, meaning electrolyte ions or electrolysis products do not damage them. As a result, they are utilised as electrodes in electrolysis.
5.2. Why does physisorption decrease with the increase of temperature?
Ans: Physisorption is an exothermic process: according to Le Chatelier's principle, equilibrium moves backward when T is increased, causing gas to escape from the solid's surface.
5.3. Why are powdered substances more effective as adsorbents than crystalline forms?
Ans: In comparison to the crystalline form, the powdered version of the adsorbent has a larger surface area. As a result, it will be more effective as an adsorbent.
5.4. In the process of Haber, we react with methane and steam to obtain hydrogen. This is done in the presence of Nio that acts as a catalyst. The process is also referred to as steam reforming. Why is it important to remove CO when Haber's process obtains ammonia?
Ans: CO is poisonous to the catalyst in Haber's method used to make NH3. As a result, it must be removed.
5.5 Why is the ester hydrolysis slow initially and becomes faster after some time?
Ans: The ester hydrolysis takes place as follows: the reaction is autocatalysed by the acid produced in the process. As a result, after some time, the reaction becomes faster.
5.6. What is the role of desorption in the process of catalysis?
Ans: Adsorbed reactant species mix to generate products in heterogeneous catalysis on a metal surface. They must be desorbed from the surface for more reactants to be accommodated on the catalyst's surface. As a result, desorption plays a unique role in the catalysis process.
5.7. What modification can you suggest in the Hardy Schulze law?
Ans: According to the Hardy Schulze Law, the coagulating ion has the opposite charge as the colloidal particles. Coagulation happens due to the neutralisation of the charge on colloidal particles. This law is modified as follows: when oppositely charged sols are blended in suitable proportions to neutralise each other's charges, both sols coagulate.
5.8. Why is it essential to wash a residue with water before estimating it quantitatively?
Ans: Ionic reactions produce precipitates in most cases. Some reactant ions may be adsorbed or adhere to the surface of the precipitate particles. These can be eliminated by periodically washing the residue in water. If these ions are not eliminated, weighing errors may occur quantitatively when the sediment is estimated.
5.1. Distinguish between the meaning of the terms adsorption and absorption. Give one example of each.
Ans: Adsorption is the process of a solid (or a liquid) attracting and keeping the molecules of a substance on its surface, resulting in a more significant concentration of the molecules on the surface. Adsorption is not the same as absorption. The material is equally distributed throughout the body of a solid or a liquid during absorption. When NH3 comes into contact with H20, it is adsorbed on the charcoal, but when it comes into contact with H20, it is absorbed by generating a homogeneous concentration NH4OH solution.
5.4. What factors influence the adsorption of a gas on a solid?
Ans: Physical adsorption is defined as the adsorption of a gas on a solid surface. The following factors have an impact on it:
● The adsorbent's nature
● The adsorbate's nature
● The adsorbent's surface area
● Activation of the adsorbent
● Pressure Effect
● Temperature Effect
A detailed explanation is as follows:
● Adsorbate nature: The same gas is adsorbed to varying degrees by different solids at the same temperature. In addition, the more the surface area of the adsorbent, the more gas is absorbed.
● The adsorbent's nature: At the same temperature, different gases are absorbed to varying degrees by different substances. The amount adsorbed increases as the gas's critical temperature rises.
● Adsorbent surface area: The amount of surface area available for adsorption per gram of adsorbent increases the adsorption extent. Because the more significant the surface area, the greater the adsorption, porous or powdered adsorbents are utilised.
● Adsorbent activation refers to boosting an adsorbent's absorbing capability by expanding its surface area. It is carried out by:
● Eliminating gases already adsorbed sectioning the adsorbent in smaller parts roughening the adsorbent's surface
● The adsorption of gas rises with pressure at a constant temperature.
● Temperature – because adsorption is only an exothermic process, we may use Le Chatelier's principle to determine that adsorption decreases as temperature rises.
5.6. What do you understand about the activation of adsorbent? How is it achieved?
Ans: Increasing the adsorbent's adsorbent power is referred to as activation. This is accomplished by increasing surface area and the number of pores and empty sites (active centres) in every unit area. Activation can be accomplished in a variety of ways.
These are a few NCERT surface chemistry solutions to have a basic overview of the topic.
Many fundamental chemical processes rely on surface chemistry, including biochemical reactions at biological interfaces present in cell walls and membranes, electronics at the surfaces and interfaces of computer microchips, and heterogeneous catalysts found in catalytic converters.
Surface chemistry plays a unique role in developing and operating numerous technologies that are crucial to our energy and environmental futures. Solar cells, chemical and biochemical sensors, microelectronics, prosthetic medical devices, reflecting and protective coatings, opticals, computer chips, electro-optics, optoelectronic devices, and adhesives all require thin films to be designed and manufactured. These involve the process and concepts of surface chemistry.
The manufacture and operation of sorbents, solid reactants, catalysts to synthesise clean fuels and chemicals, pollution cleaning, photocatalysts, fuel cells, and batteries all rely on surface chemistry. Refer to the above-mentioned NCERT solutions for class 12 surface chemistry for more understanding.
There are various video lectures and assignments on surface chemistry on the MSVgo app. Students may learn more about surface chemistry and excel in the concept by downloading the MSVgo app.