A redox reaction is a chemical reaction in which the oxidation states of the reacting entities undergo some change. Such reactions usually involve the formal or actual transfer of electrons between two reacting entities. The chemical species that undergoes oxidation and loses electrons is called the reducing agent whereas the chemical entity that undergoes reduction and gains electrons is referred to as an oxidizing agent.
Basically, redox reactions are chemical reactions that involve both oxidation and reduction. Several reactions in the field of organic chemistry are known to be redox reactions since they involve changes in the oxidation states of the reacting entities. However, many of these reactions do not involve distinct electron transfers. Moreover, the transfer of electrons is formal and is denoted by the aforementioned changes in oxidation states. An example of a redox reaction is the combustion of wood. When dry wood is burned in the presence of oxygen (usually present in large quantities in the air), the oxidation states of the carbon atoms that are present in the wood increase whereas the oxidation states of the atmospheric oxygen molecules decrease. Thus, carbon dioxide and water are formed as byproducts (generally). In this chemical reaction, oxygen is the oxidizing agent that undergoes reduction and gains electrons while carbon is the reducing agent that undergoes oxidation and loses electrons.
Applications of Redox Reactions in Pacemakers
In order to generate electricity, almost all batteries are known to use redox reactions because electricity is simply a stream of electrons that are being transferred from one material to another. Pacemakers, which are surgically implanted machines that can control the heartbeat of a human, are known to be powered by small batteries. Therefore, the proper operation of a pacemaker is reliant on a redox reaction.
Pacemakers were initially known to be powered mostly by NiCad batteries, in which nickel and cadmium react with water. The chemical equation for this redox reaction is provided below.
Cd + 2NiOOH +2H2O → Cd(OH)2 + 2Ni(OH)2
In this redox reaction, the cadmium atom is known to be oxidized whereas the nickel atoms (that are present in the compound NiOOH) are known to be reduced. With the exception of water, all the reacting entities and the products in this redox reaction exist in the solid state. This allows NiCad batteries to be capable of being recharged several hundreds of times before they finally stop operating. However, it is important to note that NiCad batteries are relatively heavy batteries and are, therefore, difficult to be carried around in a pacemaker. This is the reason why the relatively lighter lithium/iodine battery is more feasible for use in pacemakers. In the lithium-iodine battery, the lithium atoms undergo oxidation whereas the iodine atoms undergo reduction. It can be noted that while the lithium-iodine battery cannot be recharged, the lifetime offered by this battery lasts up to 10 years. To learn more about redox reactions and other interesting concepts in chemistry such as vapour pressure, subscribe to the BYJU’S YouTube channel and enable notifications.