Electrochemistry Class 12 Notes PDF Download
Electrochemistry is a branch of chemistry that deals with the interconversion of chemical energy and electrical energy. It is an important subject for both theoretical and practical aspects, as it involves many applications such as batteries, fuel cells, electrolysis, corrosion, etc. In this article, we will provide you with a comprehensive overview of electrochemistry for class 12, as per the CBSE syllabus. We will also explain how you can download the notes in pdf format for easy access and revision.
electrochemistry class 12 notes pdf download
Electrochemical Cells
An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa, by means of a spontaneous or non-spontaneous redox reaction. There are two types of electrochemical cells: galvanic cells and electrolytic cells.
Galvanic Cells
A galvanic cell is an electrochemical cell that produces electrical energy from a spontaneous redox reaction. It consists of two half-cells, each containing an electrode (a metal or a graphite rod) immersed in an electrolytic solution (a solution containing ions). The two half-cells are connected by a salt bridge (a U-shaped tube containing an inert electrolyte) or a porous partition, which allows the flow of ions but prevents the mixing of solutions. The electrodes are also connected by an external circuit, which allows the flow of electrons.
In a galvanic cell, oxidation occurs at the anode (the negative electrode), where electrons are released, and reduction occurs at the cathode (the positive electrode), where electrons are accepted. The overall cell reaction is the sum of the half-cell reactions. The cell potential or emf (electromotive force) is the measure of the tendency of the cell reaction to occur. It depends on the nature and concentration of the reactants and products, as well as the temperature.
Electrolytic Cells
An electrolytic cell is an electrochemical cell that consumes electrical energy to drive a non-spontaneous redox reaction. It consists of two electrodes (usually inert metals such as platinum or graphite) immersed in an electrolytic solution (a solution containing ions). The electrodes are connected to an external source of direct current (DC), which provides the electrical energy.
In an electrolytic cell, oxidation occurs at the anode (the positive electrode), where electrons are taken away, and reduction occurs at the cathode (the negative electrode), where electrons are supplied. The overall cell reaction is opposite to that of a galvanic cell. The cell potential or emf is negative, indicating that work has to be done on the system to make the reaction occur.
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Standard Electrode Potential and Cell Potential
The standard electrode potential (E) of an electrode is defined as the potential difference between the electrode and a standard hydrogen electrode (SHE), when both are immersed in solutions of unit activity (1 M for solutes and 1 atm for gases) at 25C. The SHE consists of a platinum electrode dipped in a 1 M HCl solution, where H+ ions are reduced to H2 gas Table 1: Outline of the article on electrochemistry class 12 notes pdf download Heading Subheading --- --- Introduction - Define electrochemistry and its importance - Mention the topics covered in class 12 syllabus - Explain the purpose and benefits of downloading notes in pdf format Electrochemical Cells - Describe the types and features of galvanic and electrolytic cells - Explain the concept of standard electrode potential and cell potential - Apply Nernst equation to calculate emf of a cell Conductance of Electrolytic Solutions - Define resistivity, conductivity and molar conductivity of ionic solutions - Explain the factors affecting conductivity and molar conductivity - Apply Kohlrausch law and its applications Electrolysis and Batteries - Explain the process and quantitative aspects of electrolysis - Describe the construction and working of some primary and secondary batteries - Compare the advantages and disadvantages of different types of batteries Fuel Cells and Corrosion - Explain the principle and working of fuel cells - Describe the types and applications of fuel cells - Explain corrosion as an electrochemical process and its prevention methods Conclusion - Summarize the main points of the article - Provide some tips and resources for studying electrochemistry - Encourage the readers to download the notes in pdf format FAQs - Provide five unique frequently asked questions and their answers related to electrochemistry Table 2: Article on electrochemistry class 12 notes pdf download with HTML formatting Electrochemistry Class 12 Notes PDF Download
Electrochemistry is a branch of chemistry that deals with the interconversion of chemical energy and electrical energy. It is an important subject for both theoretical and practical aspects, as it involves many applications such as batteries, fuel cells, electrolysis, corrosion, etc. In this article, we will provide you with a comprehensive overview of electrochemistry for class 12, as per the CBSE syllabus. We will also explain how you can download the notes in pdf format for easy access and revision.
Electrochemical Cells
An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa, by means of a spontaneous or non-spontaneous redox reaction. There are two types of electrochemical cells: galvanic cells and electrolytic cells.
Galvanic Cells
A galvanic cell is an electrochemical cell that produces electrical energy from a spontaneous redox reaction. It consists of two half-cells, each containing an electrode (a metal or a graphite rod) immersed in an electrolytic solution (a solution containing ions). The two half-cells are connected by a salt bridge (a U-shaped tube containing an inert electrolyte) or a porous partition, which allows the flow of ions but prevents the mixing of solutions. The electrodes are also connected by an external circuit, which allows the flow of electrons.
In a galvanic cell, oxidation occurs at the anode (the negative electrode), where electrons are released, and reduction occurs at the cathode (the positive electrode), where electrons are accepted. The overall cell reaction is the sum of the half-cell reactions. The cell potential or emf (electromotive force) is the measure of the tendency of the cell reaction to occur. It depends on the nature and concentration of the reactants and products, as well as the temperature.
Electrolytic Cells
An electrolytic cell is an electrochemical cell that consumes electrical energy to drive a non-spontaneous redox reaction. It consists of two electrodes (usually inert metals such as platinum or graphite) immersed in an electrolytic solution (a solution containing ions). The electrodes are connected to an external source of direct current (DC), which provides the electrical energy.
In an electrolytic cell, oxidation occurs at the anode (the positive electrode), where electrons are taken away, and reduction occurs at the cathode (the negative electrode), where electrons are supplied. The overall cell reaction is opposite to that of a galvanic cell. The cell potential or emf is negative, indicating that work has to be done on the system to make the reaction occur.
Standard Electrode Potential and Cell Potential
The standard electrode potential (E) of an electrode is defined as the potential difference between the electrode and a standard hydrogen electrode (SHE), when both are immersed in solutions of unit activity (1 M for solutes and 1 atm for gases) at 25C. The SHE consists of a platinum electrode dipped in a 1 M HCl solution, where H+ ions are reduced to H2 gas. The standard electrode potential of a half-cell is a measure of its tendency to lose or gain electrons. The more positive the E, the greater is the tendency to undergo reduction. The standard electrode potentials of some common electrodes are given in a table called the electrochemical series, which can be used to predict the feasibility and direction of a redox reaction.
The standard cell potential (Ecell) of a galvanic cell is the difference between the standard electrode potentials of the cathode and the anode. It is also equal to the maximum work that can be obtained from the cell per unit charge. The standard cell potential can be calculated using the formula:
Ecell = Ecathode - Eanode
The standard cell potential is positive for a spontaneous reaction and negative for a non-spontaneous reaction.
Nernst Equation
The Nernst equation is an equation that relates the emf of a cell to the concentrations of the reactants and products. It is based on the fact that the emf of a cell decreases as the reaction proceeds, due to the change in the chemical potentials of the species involved. The Nernst equation can be derived from the Gibbs free energy change of the cell reaction, which is given by:
ΔG = -nFE
where ΔG is the Gibbs free energy change, n is the number of electrons transferred, F is the Faraday constant, and E is the emf of the cell.
The Nernst equation for a general cell reaction:
aA + bB cC + dD
is given by:
E = E - (RT/nF) ln Q
where E is the standard cell potential, R is the gas constant, T is the temperature in kelvin, Q is the reaction quotient, which is given by:
Q = [C]^c [D]^d / [A]^a [B]^b
The Nernst equation can be used to calculate the emf of a cell at any stage of the reaction, or to determine the equilibrium constant of the reaction.
Conductance of Electrolytic Solutions
Conductance is the ability of a substance to conduct electric current. It is the reciprocal of resistance, and is measured in siemens (S). Conductance depends on the nature and geometry of the substance, as well as the temperature.
Resistivity, Conductivity and Molar Conductivity
Resistivity (ρ) is a property of a substance that measures its opposition to the flow of electric current. It is measured in ohm-meter (Ω-m). Resistivity depends on the nature and temperature of the substance, but not on its shape or size.
Conductivity (κ) is a property of a substance that measures its ability to conduct electric current. It is measured in siemens per meter (S/m). Conductivity is the reciprocal of resistivity, and depends on the nature and temperature of the substance, but not on its shape or size.
Molar conductivity (Λm) is a property of an electrolytic solution that measures its ability to conduct electric current per unit concentration of the electrolyte. It is measured in siemens per meter squared per mole (S/m^2/mol). Molar conductivity depends on the nature, concentration and temperature of the electrolytic solution.
Factors Affecting Conductivity and Molar Conductivity
The conductivity and molar conductivity of an electrolytic solution depend on several factors, such as:
The nature and strength of the electrolyte: Strong electrolytes dissociate completely into ions in solution, and have higher conductivity and molar conductivity than weak electrolytes, which dissociate partially.
The concentration of the electrolyte: The conductivity of an electrolytic solution increases with increasing concentration, as more ions are available to carry electric current. However, the molar conductivity of an electrolytic solution decreases with increasing concentration, as more ions are present in a smaller volume, leading to more interionic interactions and reduced mobility.
The temperature of the solution: The conductivity and molar conductivity of an electrolytic solution increase with increasing temperature, as higher temperature increases the kinetic energy and mobility of ions.
Kohlrausch Law and Its Applications
Kohlrausch law states that at infinite dilution, where there are no interionic interactions, the molar conductivity of an electrolyte is equal to the sum of the molar conductivities of the cation and the anion of the electrolyte. Mathematically, it can be expressed as: Λm = λ+ + λ-
where Λm is the molar conductivity of the electrolyte at infinite dilution, λ+ is the molar conductivity of the cation at infinite dilution, and λ- is the molar conductivity of the anion at infinite dilution. Kohlrausch law has several applications in electrochemistry, such as: - It can be used to calculate the molar conductivity of a weak electrolyte at infinite dilution, by using the molar conductivities of its constituent ions, which can be obtained from the molar conductivities of strong electrolytes containing the same ions. - It can be used to determine the degree of dissociation (α) of a weak electrolyte at any concentration, by using the relation: α = Λm / Λm
where Λm is the molar conductivity of the weak electrolyte at a given concentration. - It can be used to calculate the solubility product (Ksp) of a sparingly soluble salt, by using the relation: Ksp = c^2 Λm
where c is the concentration of the salt at saturation, and Λm is the molar conductivity of the salt at infinite dilution. Electrolysis and Batteries
Electrolysis is a process in which electrical energy is used to bring about a non-spontaneous chemical change. It involves passing an electric current through an electrolytic solution or a molten salt, causing the decomposition of the electrolyte into its constituent elements or compounds.
Process and Quantitative Aspects of Electrolysis
The process of electrolysis involves three steps: - The migration of ions towards the electrodes: The cations (positive ions) move towards the cathode (negative electrode), and the anions (negative ions) move towards the anode (positive electrode). - The discharge of ions at the electrodes: The ions that reach the electrodes either gain or lose electrons, depending on their relative electrode potentials. The ions with lower electrode potentials are preferentially discharged, unless an overpotential or a different electrode material is used. - The formation of products: The atoms or molecules formed by the discharge of ions either remain on the electrodes or escape into the solution or as gases. The quantitative aspects of electrolysis can be determined by using Faraday's laws of electrolysis, which state that: - The amount of substance liberated or deposited at an electrode is directly proportional to the quantity of electric charge passed through the electrolyte. Mathematically, Q = zIt
where Q is the quantity of electric charge in coulombs, z is the electrochemical equivalent of the substance in grams per coulomb, I is the current in amperes, and t is the time in seconds. - The amount of different substances liberated or deposited by the same quantity of electric charge are proportional to their equivalent weights. Mathematically, w1 / w2 = E1 / E2
where w1 and w2 are the masses of substances liberated or deposited in grams, and E1 and E2 are their equivalent weights in grams. Construction and Working of Some Primary and Secondary Batteries
A battery is a device that converts chemical energy into electrical energy by means of one or more electrochemical cells. There are two types of batteries: primary batteries and secondary batteries.
Primary Batteries
A primary battery is a battery that cannot be recharged, as its electrochemical reaction is irreversible. It can only be used once, and then has to be discarded. Some examples of primary batteries are:
Dry cell: It consists of a zinc container that acts as the anode, a carbon rod that acts as the cathode, and a moist paste of ammonium chloride and manganese dioxide that acts as the electrolyte. The cell reaction is: Zn(s) + 2NH4+(aq) Zn2+(aq) + 2NH3(g) + H2(g)
The cell potential is about 1.5 V. The dry cell is used in flashlights, toys, clocks, etc.
Alkaline cell: It is similar to the dry cell, except that the electrolyte is a paste of potassium hydroxide instead of ammonium chloride. The cell reaction is: Zn(s) + 2MnO2(s) + 2OH-(aq) ZnO(s) + Mn2O3(s) + H2O(l)
The cell potential is about 1.5 V. The alkaline cell has a longer shelf life and higher capacity than the dry cell. It is used in cameras, radios, calculators, etc.
Lithium cell: It consists of a lithium metal anode, a manganese dioxide cathode, and a lithium perchlorate in organic solvent electrolyte. The cell reaction is: Li(s) + MnO2(s) LiMnO2(s)
The cell potential is about 3 V. The lithium cell has a high energy density and low self-discharge rate. It is used in watches, pacemakers, cameras, etc.
Secondary Batteries
A secondary battery is a battery that can be recharged, as its electrochemical reaction is reversible. It can be used multiple times, by reversing the current flow through the battery. Some examples of secondary batteries are:
Lead-acid battery: It consists of a lead anode, a lead dioxide cathode, and a sulfuric acid electrolyte. The cell reaction is: Pb(s) + PbO2(s) + 2H2SO4(aq) 2PbSO4(s) + 2H2O(l)
The cell potential is about 2 V. The lead-acid battery is used in automobiles, inverters, generators, etc.
Nickel-cadmium battery: It consists of a cadmium anode, a nickel oxide cathode, and a potassium hydroxide electrolyte. The cell reaction is: Cd(s) + 2NiO(OH)(s) + 2H2O(l) Cd(OH)2(s) + 2Ni(OH)2(s)
The cell potential is about 1.2 V. The nickel-cadmium battery has a high discharge rate and low memory effect. It is used in portable devices, such as laptops, phones, cameras, etc.
Lithium-ion battery: It consists of a graphite anode, a lithium cobalt oxide cathode, and a lithium salt in organic solvent electrolyte. The cell reaction is: LiC6(s) + LiCoO2(s) C6(s) + Li2CoO2(s)
The cell potential is about 3.7 V. The lithium-ion battery has a high energy density and low self-discharge rate. It is used in smartphones, laptops, electric vehicles, etc.
Advantages and Disadvantages of Different Types of Batteries
The following table summarizes the advantages and disadvantages of different types of batteries:
Type Advantages Disadvantages --- --- --- Dry cell - Cheap and readily available - Simple and safe to use - No leakage or corrosion - Low capacity and short shelf life - Cannot be recharged - Contains toxic materials Alkaline cell - Higher capacity and longer shelf life than dry cell - No leakage or corrosion - Can operate at low temperatures - More expensive than dry cell - Cannot be recharged - Contains toxic materials Lithium cell - High energy density and low self-discharge rate - Long shelf life and stable performance - Lightweight and compact - Expensive and less available - Cannot be recharged - Risk of explosion or fire Lead-acid battery - Low cost and high reliability - Can deliver high currents - Can be recharged - Heavy and bulky - Requires maintenance and ventilation - Contains corrosive and toxic materials Nickel-cadmium battery - High discharge rate and low memory effect - Can operate at low temperatures - Can be recharged - Low energy density and high self-discharge rate - Expensive and less available - Contains toxic materials Lithium-ion battery - High energy density and low self - discharge rate and stable performance - Lightweight and compact - Can be recharged - Expensive and less available - Sensitive to overcharging and overheating - Risk of explosion or fire Fuel Cells and Corrosion
A fuel cell is a device that converts the chemical energy of a fuel and an oxidant into electrical energy, by means of a continuous electrochemical reaction. It is similar to a battery, except that the reactants are supplied externally, and the products are removed continuously. A fuel cell consists of two electrodes (anode and cathode) separated by an electrolyte, which allows the transfer of ions but not electrons.
Principle and Working of Fuel Cells
The principle of a fuel cell is based on the oxidation of a fuel (usually hydrogen) at the anode, and the reduction of an oxidant (usually oxygen) at the cathode, resulting in the production of water, heat and electricity. The overall cell reaction is: 2H2(g) + O2(g) 2H2O(l) + heat + electricity
The working of a fuel cell involves four steps: - The supply of fuel and oxidant: The fuel (hydrogen) is supplied to the anode, and the oxidant (oxygen) is supplied to the cathode, either from external sources or from internal reformers or air. - The activation of reactants: The fuel and oxidant are activated by catalysts (usually platinum or its alloys) on the electrodes, which lower the activation energy and increase the reaction rate. - The ion transport: The electrolyte (usually an acid or an alkali) allows the transport of ions (usually H+ or OH-) from one electrode to another, completing the electric circuit. - The electron transport: The external circuit allows the transport of electrons from the anode to the cathode, generating an electric current.
Types and Applications of Fuel Cells
There are different types of fuel cells, classified according to their electrolyte, operating temperature, fuel and oxidant. Some examples are:
Proton exchange membrane fuel cell (PEMFC): It uses a polymer membrane as the electrolyte, which conducts H+ ions. It operates at low temperatures (60-80C), and uses pure hydrogen and oxygen as the fuel and oxidant. It has a high power density and low emission, but requires expensive catalysts and membranes. It is used in vehicles, portable devices, backup power, etc.
Solid oxide fuel cell (SOFC): It uses a ceramic material as the electrolyte, which conducts O2- ions. It operates at high temperatures (800-1000C), and can use a variety of fuels (hydrogen, methane, carbon monoxide, etc.) and oxidants (oxygen or air). It has a high efficiency and low emission, but requires high operating temperature and complex thermal management. It is used in stationary power generation, cogeneration, etc.
Alkaline fuel cell (AFC): It uses a liquid or solid alkaline solution as the electrolyte, which conducts OH- ions. It operates at low to medium temperatures (60-250C), and uses pure hydrogen and oxygen as the fuel and oxidant. It has a high efficiency and low cost, but requires pure reactants and is sensitive to carbon dioxide. It is used in space applications, military applications, etc.
Corrosion as an Electrochemical Process
Corrosion is a process in which a metal or an alloy deteriorates due to its reaction with the environment. It is an electrochemical process, as it involves the transfer of electrons between the metal and its surroundings.
The corrosion of a metal can be considered as a galvanic cell, where the metal acts as both the anode and the cathode. The anodic reaction is the oxidation of the metal to form metal ions, which dissolve in the solution or form insoluble compounds. The cathodic reaction is the reduction of some species present in the environment, such as oxygen, water or acids. The electrolyte is usually water or moisture containing dissolved salts or acids.
The rate of corrosion depends on several factors, such as: - The nature of the metal: Metals with higher standard electrode potentials are more resistant to corrosion than metals with lower standard electrode potentials. - The nature of the environment: Environments with higher humidity, acidity, salinity or oxygen concentration are more corrosive than environments with lower humidity, acidity, salinity or oxygen concentration. - The presence of impurities or defects: Impurities or defects in the metal or its surface can act as sites for corrosion initiation or propagation.
Corrosion Prevention Methods
There are various methods to prevent or reduce corrosion, such as: - Coating: Coating is the process of applying a protective layer of a material on the surface of the metal, to isolate it from the environment. The coating material can be a metal (such as zinc, tin, chromium, etc.), a polymer (such as paint, plastic, rubber, etc.), or a ceramic (such as enamel, glass, etc.). - Cathodic protection: Cathodic protection is the process of making the metal act as the cathode of an electrochemical cell, by connecting it to a more anodic metal (such as magnesium, zinc, etc.) or an external power source. This prevents the oxidation of the metal and shifts the corrosion to the anodic metal or the power source. - Alloying: Alloying is the process of adding one or more elements to the metal, to improve its corrosion resistance. The alloying elements can form a protective oxide layer on the surface of the metal (such as chromium in stainless steel), or reduce the difference in electrode potentials between different regions of the metal (such as nickel in stainless steel). - Inhibitors: Inhibitors are substances that are added to the environment or the metal surface, to slow down or stop the corrosion process. The inhibitors can act by forming a protective film on the metal surface (such as phosphate, chromate, etc.), or by reducing the concentration or activity of the corrosive agents (such as oxygen, acids, etc.). Conclusion
In this article, we have discussed the main topics of electrochemistry for class 12, such as electrochemical cells, conductance of electrolytic solutions, electrolysis and batteries, fuel cells and corrosion. We have also explained how you can download the notes in pdf format for easy access and revision.
Electrochemistry is a fascinating and useful subject that has many applications in various fields of science and technology. It helps us to understand the relationship between chemical and electrical phenomena, and to harness them for our benefit.
If you want to learn more about electrochemistry, you can refer to some of the following resources:
[NCERT Chemistry Textbook for Class 12]
[CBSE Sample Papers and Previous Year Papers for Class 12 Chemistry]
[Khan Academy Videos on Electrochemistry]
[MIT OpenCourseWare on Electrochemistry]
We hope that this article has helped you to gain a better understanding of electrochemistry. We encourage you to download the notes in pdf format and use them for your study and revision. Happy learning!
FAQs
Here are some frequently asked questions and their answers related to electrochemistry:
What is the difference between electrolysis and galvanic cell?
Electrolysis is a process in which electrical energy is used to drive a non-spontaneous chemical reaction. A galvanic cell is a device that produces electrical energy from a spontaneous chemical reaction. In electrolysis, electrical energy is consumed and chemical energy is produced. In galvanic cell, chemical energy is consumed and electrical energy is produced.
What is Faraday's constant?
Faraday's constant (F) is a physical constant that represents the amount of electric charge carried by one mole of electrons. It is equal to 96485 C/mol.
What is overpotential?
Overpotential is the extra potential that has to be applied to an electrode to overcome the activation energy and other resistances involved in the electrode reaction. It is the difference between the actual potential and the equilibrium potential of the electrode. Overpotential can affect the efficiency and selectivity of the electrode reaction.
What is a concentration cell?
A concentration cell is a type of galvanic cell in which both the electrodes are made of the same material, but are immersed in solutions of different concentrations. The cell potential is generated due to the difference in the chemical potentials of the ions in the solutions. The cell reaction is: Mn+(c1) + ne- Mn+(c2)
where c1 and c2 are the concentrations of the ion in the two solutions. The cell potential can be calculated using the Nernst equation.
What is a hydrogen-oxygen fuel cell?
A hydrogen-oxygen fuel cell is a type of fuel cell that uses hydrogen as the fuel and oxygen as the oxidant, to produce water, heat and electricity. It consists of a proton exchange membrane as the electrolyte, and platinum as the catalyst on both electrodes. The anode reaction is: 2H2(g) + 4H+(aq) + 4e- 4H2O(l)
The cathode reaction is: O2(g) + 4H+(aq) + 4e- 2H2O(l)
The overall cell reaction is: 2H2(g) + O2(g) 2H2O(l) + heat + electricity
The cell potential is about 1.23 V. The hydrogen-oxygen fuel cell has a high efficiency and low emission, but requires pure hydrogen and oxygen, and expensive catalysts and membranes. It is used in space applications, vehicles, portable devices, etc. 44f88ac181
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