Electrochemistry - SS2 Chemistry Past Questions and Answers - page 3

Electrolysis is a process that uses an electric current to drive a non-spontaneous chemical reaction. It involves the decomposition of an electrolyte (a compound that conducts electricity when dissolved or molten) into its constituent ions at the electrodes. The positive ions (cations) migrate towards the cathode (negative electrode) and gain electrons, while the negative ions (anions) migrate towards the anode (positive electrode) and lose electrons.

The process of electrolysis has various applications, including:

●     Electroplating: Electrolysis is used to deposit a layer of metal onto a substrate, providing protection, improved appearance, or specific properties. For example, electroplating is commonly used to coat objects with a layer of gold, silver, or other metals.

●     Electrorefining: Electrolysis is employed in the purification of metals, such as copper. Impure metal is used as the anode, and the pure metal is deposited on the cathode during the electrolytic process.

●     Electrolytic cells: Electrolytic cells are used in the production of chemicals and metals. For instance, the electrolysis of water can generate hydrogen and oxygen gases, which have numerous industrial applications.

Faraday's laws of electrolysis provide a quantitative understanding of the relationships between the amount of substance deposited or liberated during electrolysis and the quantity of electricity passed through the cell.

●     Faraday's First Law: The amount of substance liberated or deposited at an electrode is directly proportional to the quantity of electricity passing through the cell. The relationship is expressed by the equation:

Amount of substance = (Current × Time) / Faraday's constant

●     Faraday's Second Law: The amounts of different substances liberated or deposited by the same quantity of electricity are directly proportional to their respective chemical equivalent weights. The chemical equivalent weight is the mass of a substance that is liberated or deposited by one Faraday of charge.

These laws highlight the relationship between the flow of electric charge (current) and the amount of substance involved in the electrolytic reaction. They enable the calculation of the mass of the substance produced or consumed during electrolysis based on the current, time, and chemical properties.

By applying Faraday's laws, scientists and engineers can precisely control and predict the outcomes of electrolytic processes. The laws provide a foundation for understanding the quantitative aspects of electrolysis and contribute to the advancement of various technological applications involving electrochemical reactions.

The efficiency of electrolysis, which refers to the extent to which the desired electrochemical reaction occurs, can be influenced by several factors. Optimising these factors is crucial to enhance the efficiency of the electrolytic process. Some key factors include:

1.    Current Density: The current density, or the current per unit area of the electrode surface, affects the rate of the electrochemical reactions. Higher current densities can lead to increased efficiency but may also result in undesirable side reactions or electrode degradation. The current density should be optimised based on the specific electrolysis process.

2.    Electrolyte Concentration: The concentration of the electrolyte can influence the conductivity and reaction rate. An optimal electrolyte concentration ensures sufficient ion mobility and allows for efficient electrolysis. However, excessively high concentrations may lead to increased resistance or undesirable side reactions.

3.    Temperature: The temperature of the electrolyte affects the reaction rate and the efficiency of electrolysis. Generally, higher temperatures increase reaction rates but can also lead to increased energy consumption and potential degradation of the electrode materials. The temperature should be optimised to balance these factors.

4.    Electrode Material: The choice of electrode material is important for achieving efficient electrolysis. The material should possess good conductivity, stability, and resistance to corrosion or degradation. Selection of suitable electrode materials can enhance the efficiency and longevity of the electrolytic process.

Overpotential, also known as polarisation, refers to the additional potential required to drive an electrochemical reaction compared to the theoretical potential predicted by thermodynamics. Overpotential occurs due to various factors such as resistance within the electrolyte, activation energy requirements, and surface reactions at the electrodes.

Overpotential can negatively impact the efficiency of electrolysis by increasing energy consumption and decreasing the reaction rate. Minimising overpotential is crucial for optimising the efficiency of the electrolytic process. This can be achieved through careful electrode design, selection of suitable electrolytes, and controlling the operating conditions.

Efficiency in electrolysis is a complex interplay of multiple factors, and optimization requires a thorough understanding of the specific electrochemical system. By addressing factors such as current density, electrolyte concentration, temperature, electrode material, and minimising overpotential, the efficiency of electrolysis processes can be enhanced, leading to improved productivity and reduced energy consumption.