Trystan Casey
There are various types of electrical reactions, and they play a crucial role in our everyday lives. An electrical reaction, or an electrochemical reaction, is a process caused or accompanied by the passage of an electric current, often involving the transfer of electrons between two substances. For example, the simple act of turning on a torch involves a continuous flow of electrons through an external circuit. In nature, the generation of chemical energy through photosynthesis is an electrochemical process. In industry, electrochemical reactions are used in the coating of objects with metals through electrodeposition and the detection of alcohol in drunk drivers.
| Characteristics | Values |
|---|---|
| Definition | Any process caused or accompanied by the passage of an electric current and involving the transfer of electrons between two substances |
| Conversion of energy | The conversion of chemical energy into electrical energy, and vice versa |
| Examples | Batteries, fuel cells, electrolysis, redox reactions, corrosion, electroplating, electropolishing |
| Components | Anode (negative electrode), cathode (positive electrode), electrolyte |
| Other | The energy of an electric current can be used to bring about chemical reactions that would not otherwise occur |
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What You'll Learn
Electrochemical reactions
These reactions are central to our understanding of electricity and its applications, especially in batteries. A battery is made up of two electrodes, the anode (negative) and the cathode (positive), which are generally different types of metals or other chemical compounds. The anode provides electrons that flow through a wire to the cathode. This flow of electrons is what we call electricity, and it can be harnessed to power our devices.
The reactions at the anode and cathode produce new chemical products, which can create resistance, slowing down the reaction and causing the battery to lose power. These reactions can be reversed by applying a voltage, which results in the deposition of metal at the anode and the formation of ions at the cathode.
Corrosion, such as the rusting of iron, is also an electrochemical process. It is a series of redox reactions involving the metal and oxygen and water in the environment.
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Batteries
The electrochemical cell in a battery is composed of two electrodes, the anode (negative electrode) and the cathode (positive electrode), which are generally different types of metals or other chemical compounds. The anode produces a reaction with a significantly lower (more negative) standard potential than the cathode. This results in electrons being attracted to the cathode from the anode, and when provided with an easy pathway to get there—a conducting wire—we can harness their energy to provide electrical power.
The capacity of a battery depends directly on the quantity of electrode and electrolyte material inside the cell. Batteries can be single-use (primary or disposable) or rechargeable (secondary). Single-use batteries cannot be recharged as their electrochemical reactions are non-reversible, whereas rechargeable batteries undergo electrochemical reactions that can be readily reversed as the components that react are not completely used up.
There are many types of batteries, including Leclanché dry cells, alkaline batteries, lithium-ion batteries, nickel-cadmium batteries, and lead-acid batteries. The choice of battery depends on the specific application and requirements, such as energy capacity, rechargeability, and output-to-mass ratio.
The performance of batteries can be impacted by various factors such as temperature, charge cycles, and internal chemical reactions. For example, warmer temperatures can speed up side chemical reactions, reducing the battery's performance, and high-rate charging and discharging can lead to a disordered crystal structure, resulting in decreased efficiency.
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Corrosion
In the context of corrosion, the term "anode" refers to the portion of the metal surface that is actively corroding, while the term "cathode" refers to the metal surface that consumes the electrons generated by the corrosion reaction. This electron transfer process is also known as anodic and cathodic reactions, respectively.
A specific type of corrosion is galvanic corrosion, also known as bimetallic corrosion or dissimilar metal corrosion. This occurs when one metal corrodes preferentially in electrical contact with another dissimilar metal, in the presence of an electrolyte. The dissimilar metals have different electrode potentials, and when they come into contact, the more reactive metal acts as the anode and corrodes more rapidly, while the less reactive metal acts as the cathode and experiences inhibited corrosion.
Another example of galvanic corrosion is the cleaning of silverware by immersing it in a hot electrolytic bath with a piece of aluminium foil. The aluminium, being more reactive, corrodes and strips the sulfur atoms from the silver sulfide formed on the silverware, leaving behind elemental silver.
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Fuel cells
The fundamental structure of a fuel cell consists of an anode, cathode, and an electrolyte membrane. During operation, hydrogen is passed through the anode, while oxygen is directed through the cathode. At the anode, a catalyst divides the hydrogen molecules into electrons and positively charged protons. The protons selectively pass through the porous electrolyte membrane, while the electrons are forced through a circuit, creating an electric current and heat. Subsequently, at the cathode, the protons, electrons, and oxygen unite to form water molecules.
There are several types of fuel cells, each with unique characteristics. Proton Exchange Membrane Fuel Cells (PEMFCs), for instance, utilise a polymer membrane as an electrolyte and platinum as a catalyst. PEMFCs can operate at relatively cooler temperatures, typically between 80 to 200 degrees Fahrenheit, due to their use of precious metals. In contrast, Molten Carbonate Fuel Cells (MCFCs) function at much higher temperatures, surpassing 1200 degrees Fahrenheit, enabling the use of non-platinum catalysts and internal reforming of natural gas into hydrogen. MCFCs are commonly employed in stationary applications, providing primary and backup power to utilities and businesses.
The development of fuel cells faces several critical challenges, including cost, performance, and durability. Platinum, a costly component in direct hydrogen-fuelled polymer electrolyte membrane fuel cells, significantly impacts overall expenses. Researchers are exploring strategies to reduce platinum content and improve the efficiency and durability of fuel cell components to address these challenges.
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Redox reactions
In a redox reaction, there are two components: oxidation and reduction. Oxidation is the loss of electrons from a substance, resulting in an increase in its oxidation state. This occurs when a substance donates electrons to another substance, which becomes reduced. Reduction, on the other hand, is the gain of electrons, leading to a decrease in oxidation state. The species that loses electrons is called the reducing agent, while the one that gains electrons is the oxidizing agent.
For example, in the reaction between hydrogen and fluorine, hydrogen is oxidized as it loses electrons, and fluorine is reduced as it gains those electrons. This results in the formation of hydrogen fluoride. Similarly, in a Daniell cell, the zinc electrode (anode) undergoes oxidation by losing electrons, while the copper electrode (cathode) gains electrons, leading to the formation of a simple battery with a spontaneous electric current.
Understanding redox reactions involves grasping the concepts of oxidation and reduction individually and then combining them in a full redox reaction. The number of electrons lost or gained during these reactions is crucial, as it determines the oxidation state of the species involved.
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Frequently asked questions
It is a process caused or accompanied by the passage of an electric current and involves the transfer of electrons between two substances, one solid and the other a liquid.
The generation of chemical energy through photosynthesis, the production of metals like aluminium and titanium from ores, and the detection of alcohol in drunk drivers through the redox reaction of ethanol are all electrochemical processes.
Chemical reactions are associated with a specific heat profile, whereas the Gibbs free energy of electrochemical reactions is converted directly to electricity without heat reaching the surroundings.
Batteries rely on chemical reactions to generate electricity. A continuous flow of electrons and positively charged ions occurs when a battery is being used. When the flow is halted, the chemical reactions driving the battery stop.
The anode is the negative electrode from which electrons flow to the cathode, the positive electrode. The difference in standard potential between the electrodes determines the force with which electrons travel between them.
