This blog post explains in an easy-to-understand manner how chemical cells generate electricity and how the ionization tendencies of metals determine the anode and cathode.
A chemical battery is a device that generates electricity through a chemical reaction, and the batteries we use in our daily lives are a type of chemical battery. There are various types of batteries depending on their size and shape, and they are widely used in various fields such as home, industrial, and medical use. These batteries contain specific chemicals inside, which generate electric current. Chemical batteries use a variety of materials and electrolytes to supply electricity, and these components have a significant impact on the performance and lifespan of the battery. When using a battery, the positive and negative electrodes must be correctly matched. This is a problem that is directly related to the efficiency and safety of the battery, and if connected incorrectly, the battery may not work properly or even be damaged. This is because the electrode of a chemical cell is the anode where reduction occurs to obtain electrons, and the cathode where oxidation occurs to lose electrons, and electrons move from the cathode to the anode.
The anode and cathode of a chemical cell are determined by the ionization tendency of the metal that makes up the electrode. The ionization tendency refers to the degree to which a metal is likely to lose electrons and become a cation in a solution. This is an important factor that determines the performance of the battery, and it has a significant impact on the efficiency and lifespan of the battery. Therefore, metals with a high ionization tendency dissolve easily in electrolyte solutions that conduct electricity well to become cations. A chemical battery is created by placing copper and zinc plates in a dilute sulfuric acid (H2SO4) solution and using them as electrodes. Since zinc has a greater tendency to ionize than copper, the zinc atoms on the surface of the zinc plate become cations, and the electrons that have been detached from the zinc atoms move along the conductor to the copper plate. Since the current flows in the opposite direction to the electrons, the copper plate becomes the anode and the zinc plate becomes the cathode. If you replace the zinc plate with a silver plate, replace the sulfuric acid solution with an aqueous solution of sodium chloride, and connect the copper plate and the silver plate with a wire, the copper plate becomes the cathode and the silver plate becomes the anode. This is because copper has a greater tendency to ionize than silver. As such, the anode and cathode in a chemical cell are determined by the relative magnitude of the ionization tendency of the two metals.
Chemical batteries are not just a means of storing energy, but are also seen as an important key to the efficient use of renewable energy and solving future energy problems. For example, large-scale chemical batteries can be used to store electricity generated by renewable energy sources such as solar and wind power. Unlike the small batteries we use in our daily lives, these batteries have the ability to store and supply energy on a large scale.
The tendency of a metal to ionize can be compared to the magnitude of the reaction heat. To understand this, we need to know the process by which an atom in a metal breaks away and becomes a hydrated ion. Generally, metals have a crystalline structure in which many metal atoms are combined. Metals lose electrons to become cations, and an individual ion can only be formed when a metal atom leaves the crystal. For example, one atom of metallic zinc (Zn) in an electrolyte solution leaves the solution and becomes a zinc ion (Zn2+) by losing two electrons. This reaction requires energy, so a reaction that absorbs heat occurs in the zinc metal. When a chemical reaction occurs in this way, the reaction that absorbs heat is called an endothermic reaction. Afterwards, the zinc ions are hydrated in the electrolyte solution. In this reaction, a reaction that releases energy occurs, and the reaction that releases heat is called an exothermic reaction.
In the ionization tendency of metals, the heat of reaction is determined by the amount of heat absorbed or released when a chemical reaction occurs at a constant temperature. Therefore, when comparing the ionization tendency with the heat of reaction, the heat from an endothermic reaction and the heat from an exothermic reaction are compared as a combined value. The reaction heat is indicated by a sign, and generally, the heat when an exothermic reaction occurs is indicated as positive, and the heat when an endothermic reaction occurs is indicated as negative. The degree of ionization tendency increases as the value of the reaction heat increases, so the degree of ionization tendency is related to the magnitude of the heat in an exothermic reaction and the magnitude of the heat in an endothermic reaction. The list of metal elements based on the magnitude of their ionization tendency is called the ionization sequence. The ionization sequence makes it easy to see which metal will be the anode and which will be the cathode in a chemical cell. This is an important criterion for the design and manufacture of cells, and the choice of metal according to the ionization sequence greatly affects the performance and efficiency of the cell.
