Electrochemistry

1. Electrochemical Cells:

• Types of electrochemical cells (galvanic and electrolytic)

  • Galvanic cells: Spontaneous chemical reactions that generate electricity.
  • Electrolytic cells: Electricity is used to drive non-spontaneous chemical reactions. [Ref: NCERT Class 11, Ch 10, Electrochemistry]

• Cell components (electrodes, electrolyte, salt bridge)

  • Electrodes: Positive electrode (anode) and negative electrode (cathode)
  • Electrolyte: A solution containing ions that allows the flow of current.
  • Salt bridge: A U-shaped tube filled with an electrolyte that connects the two half-cells. [Ref: NCERT Class 11, Ch 10, Electrochemistry]

• Cell potential and its calculation using standard reduction potentials

  • Cell potential (E°cell) is the difference in the standard reduction potentials of the cathode and anode.
  • E°cell = E°cathode - E°anode
  • Positive E°cell indicates a spontaneous reaction, while a negative E°cell indicates a non-spontaneous reaction. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

• Nernst equation and its applications

  • The Nernst equation relates the cell potential to the concentrations of reactants and products.
  • Ecell = E°cell - (RT/nF) ln Q
  • R is the ideal gas constant, T is the temperature, n is the number of moles of electrons transferred, F is Faraday’s constant, and Q is the reaction quotient. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

2. Redox Reactions and Electrode Processes:

• Oxidation and reduction reactions

  • Oxidation: Loss of electrons.
  • Reduction: Gain of electrons.
  • Redox reactions involve both oxidation and reduction.

• Balancing redox equations -Balancing redox equations involves adjusting the coefficients of reactants and products to ensure that the total charge on both sides of the equation is equal.

  • The half-reaction method is commonly used to balance redox equations. [Ref: NCERT Class 11, Ch 10, Electrochemistry]

• Half reactions and their role in electrochemical cells

  • Half reactions are the individual oxidation and reduction reactions that occur at the anode and cathode.
  • Half reactions help in understanding the electrode processes and calculating the overall cell potential.

• Faraday’s laws of electrolysis and stoichiometry of electrode reactions

  • Faraday’s laws relate the amount of substance produced at an electrode to the amount of electric charge passed through the electrode.
  • The first law states that the mass of substance produced is directly proportional to the amount of charge passed.
  • The second law states that the masses of different substances produced by the same amount of charge are directly proportional to their equivalent weights. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

3. Electrolysis and its Applications:

• Principles of electrolysis

  • Electrolysis is the process of using electricity to bring about chemical changes.
  • Electrolysis occurs when a direct electric current is passed through an electrolytic solution, causing the decomposition of the compound into its constituent elements or simpler compounds.

• Electrolytic refining of metals

  • Electrolytic refining is a process of purifying metals by electrolysis.
  • The impure metal is used as the anode, and a pure metal is used as the cathode.
  • The metal ions from the anode dissolve in the electrolyte and then deposit on the cathode as pure metal. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

• Electrolysis of water and other compounds

  • Electrolysis of water produces hydrogen and oxygen gases.
  • Electrolysis of other compounds, such as sodium chloride, produces various products depending on the compound.

• Industrial applications of electrolysis (chlorine production, aluminum production)

  • Electrolysis is used in the production of chlorine, hydrogen, sodium hydroxide, and aluminum.

4. Concentration Cells and Fuel Cells:

• Concentration cells and their potential

  • Concentration cells are electrochemical cells in which the reactants have different concentrations in the two half-cells.
  • The cell potential of a concentration cell depends on the concentration difference between the two half-cells.

• Fuel cells (hydrogen fuel cells) and their working principles

• Hydrogen fuel cells are electrochemical cells that convert the energy of hydrogen directly into electricity.

• Fuel cells involve the reaction of hydrogen (anode) and oxygen (cathode), producing water and generating electricity.

• Advantages and applications of fuel cells

  • Fuel cells have high efficiency and produce water as the byproduct, making them eco-friendly.
  • Fuel cells are used in various applications, including portable devices, vehicles, and power plants.

5. Corrosion and its Prevention:

• Types of corrosion (galvanic corrosion, pitting corrosion, etc.)

  • Corrosion is the deterioration of metals due to their reaction with substances in the environment.
  • Different types of corrosion include galvanic corrosion, pitting corrosion, uniform corrosion, and stress corrosion cracking. [Ref: NCERT Class 11, Ch 10, Electrochemistry]

• Factors affecting corrosion

• Methods of corrosion prevention (cathodic protection, sacrificial anodes, etc.)

  • Cathodic protection: Protecting metal surfaces by making them the cathode of an electrochemical cell.
  • Sacrificial anodes: Attaching more reactive metals (e.g., zinc) to the metal to be protected, which corrode instead of the metal. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

6. Batteries:

• Primary batteries (dry cells, alkaline batteries)

  • Primary batteries are single-use batteries in which the chemical reactions that generate electricity cannot be reversed.
  • Examples include dry cells (Leclanche cells) and alkaline batteries. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

• Secondary batteries (lead-acid batteries, lithium-ion batteries)

  • Secondary batteries are rechargeable batteries in which the chemical reactions that generate electricity can be reversed.
  • Examples include lead-acid batteries (used in automobiles) and lithium-ion batteries (used in electronic devices).

• Battery capacity and energy density

  • Battery capacity refers to the amount of charge it can store.
  • Energy density refers to the amount of energy stored per unit mass or volume of the battery.

• Applications of batteries

  • Batteries are used in various applications, including portable devices, vehicles, and power backup systems.

7. Fuel Cells:

• Working principles of fuel cells (hydrogen fuel cells, solid oxide fuel cells)

  • Fuel cells involve the electrochemical reaction between a fuel (usually hydrogen) and an oxidant (usually oxygen).
  • The reaction generates electricity, water, and heat. Solid oxide fuel cells (SOFCs) operate at high temperatures (800-1000°C) and use a solid oxide electrolyte. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

• Advantages and applications of fuel cells

  • Fuel cells have high efficiency and produce water as a byproduct, making them environmentally friendly.
  • Fuel cells are used in various applications, including vehicles, portable devices, and power plants.

8. Supercapacitors:

• Types of supercapacitors

  • Supercapacitors store electrical energy electrostatically or through ion adsorption.
  • There are two main types: electric double-layer capacitors (EDLCs) and pseudocapacitors.

• Charge storage mechanisms

  • EDLCs store charge in the electrical double layer formed at the electrode-electrolyte interface.
  • Pseudocapacitors store charge through redox reactions involving the electrode material.

• Advantages and applications of supercapacitors

  • Supercapacitors offer high power density, rapid charging and discharging, and long cycle life.
  • They are used in various applications, including energy storage systems, automotive electronics, and consumer electronics.

9. Electroplating and Electroless Plating:

• Principles of electroplating and electroless plating

  • Electroplating involves depositing a metal coating on a conductive surface by electrolysis.
  • Electroless plating, also known as chemical plating, involves depositing a metal coating without using an external electrical current.

• Electroplating of metals (copper, nickel, chromium, etc.)

  • Electroplating with metals like copper, nickel, chromium, and silver is used for various purposes such as improving corrosion resistance, enhancing appearance, and providing electrical conductivity. [Ref: NCERT Class 12, Ch 3, Electrochemistry]

• Industrial applications of electroplating and electroless plating

  • Electroplating and electroless plating find applications in industries like automotive, aerospace, jewelry, and electronics.