Wiktor Wise
The relationship between electricity and chemical changes has been studied for centuries, with the first electrochemical reactions observed in 1796. This branch of physical chemistry, known as electrochemistry, explores how electrical potential differences lead to identifiable chemical changes. Electrochemical reactions involve the movement of electrons via an electronically conducting phase, such as an external electrical circuit, between electrodes separated by an ionically conducting and electronically insulating electrolyte. These reactions can be harnessed to produce electricity, as seen in batteries, which are composed of electrochemical cells. The chemical reactions in batteries involve the flow of electrons from one electrode to another, generating an electric current. This current can then be used to power various devices, from telegraph systems in the 19th century to modern smartphones and laptops. Thus, the interplay between electricity and chemical changes has been pivotal in shaping our technological landscape.
| Characteristics | Values |
|---|---|
| Definition | Any process caused or accompanied by the passage of an electric current and involving the transfer of electrons between two substances, one solid and the other liquid. |
| Electrochemical cell | Composed of an anode and cathode in two separate solutions. |
| Electrodes | The electrode where oxidation occurs is called the anode, and the electrode where reduction occurs is called the cathode. |
| Chemical change | The deposition of a metal, the liberation of hydrogen, the formation of a basic substance, or some other chemical reduction process. |
| Electrolyte | Prepared by melting a suitable substance or by dissolving it in water or another liquid. |
| Chemical energy | Transformed into electrical energy. |
| Electrical work | The maximum possible electrical energy that could be obtained from a chemical reaction. |
| Electric current | A flow of charged particles. |
| Redox reaction | Reduction-oxidation reaction, a reaction that involves the exchange of electrons. |
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What You'll Learn
Electrochemical reactions
Electrochemical cells are composed of an anode and a cathode in two separate solutions, connected by a salt bridge and a conductive wire. The electrode where oxidation occurs is the anode, and the electrode where reduction occurs is the cathode. These terms refer to the loss or gain of electrons, respectively. The cathode is typically the positive electrode, and the anode the negative electrode.
The flow of electrons from one electrode to another provides an electric current. This flow occurs due to the presence of electrically charged atoms or groups of atoms in the electrolyte, which is a solution that is in contact with both electrodes. Different electrodes and electrolytes produce different chemical reactions, affecting how the battery works, how much energy it can store, and its voltage.
The charging of an accumulator is an example of a process of electrolysis, where a chemical change is produced by the electric current passing through it. In the discharge of the cell, the reverse chemical change occurs, with the accumulator acting as a cell that produces an electric current.
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Oxidation-reduction reactions
Redox reactions are vital to basic life functions such as photosynthesis, respiration, and corrosion or rusting. For example, during the rusting of iron, the oxidation state of iron atoms increases as they convert to an oxide, while the oxidation state of oxygen decreases as it accepts electrons released by the iron. Another example is the reaction of hydrogen peroxide (\(H_2O_2\)) with a cut, which produces oxygen and water. In this reaction, oxygen is both oxidized and reduced.
In electrochemical reactions, the oxidation and reduction processes occur simultaneously but are separated in space. These reactions are driven by an electrical potential difference, as in electrolysis, or result in a potential difference, as in an electric battery or fuel cell. During electrolysis, an electric current passing through an electrolyte can cause chemical changes at the electrodes. For instance, at the negative electrode (cathode), a metal may be deposited, or hydrogen may be liberated, while at the positive electrode (anode), the anode may dissolve, a non-metal may be liberated, or oxygen and an acidic substance may be produced.
The passage of electricity through gases generally causes chemical changes, forming a separate branch of electrochemistry. Additionally, the charging and discharging of a storage battery involve chemical changes produced by electric currents.
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Electrochemical cells
The two primary types of electrochemical cells are galvanic cells and electrolytic cells. A galvanic cell can be used to provide energy to do work, like the common "battery" we use in flashlights and electrical devices. An electrolytic cell is an electrochemical cell in which applied electrical energy drives a non-spontaneous redox reaction. They are often used to decompose chemical compounds, in a process called electrolysis.
The first electrochemical reactions studied in 1796 were those in the cell of silver and zinc plates with blotting paper wetted by an aqueous salt solution between them. These cells were constructed by Italian scientist Alessandro Volta, for whom the term "volt" was named.
In a full electrochemical cell, species from one half-cell lose electrons (oxidation) to their electrode, while species from the other half-cell gain electrons (reduction) from their electrode. As electrons flow from one half-cell to the other through an external circuit, a difference in charge is established.
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Electric current
Electrochemical reactions involve the passage of an electric current, often accompanied by the transfer of electrons between two substances, typically a solid and a liquid. These reactions are driven by an electrical potential difference, as seen in electrolysis, or they can result in a potential difference following a chemical reaction, as observed in electric batteries or fuel cells.
The first electrochemical reactions studied were conducted by Italian scientist Alessandro Volta in 1796, using a cell of silver and zinc plates with blotting paper wetted by an aqueous salt solution. This cell was the first primary battery used for electricity production.
In an electrochemical cell, electrons are generated by a chemical reaction occurring at one electrode, and they subsequently flow to the other electrode. This process involves the reduction and oxidation (redox) of the electrodes. At the anode, the electrode reacts with the electrolyte, producing electrons that accumulate at the anode. At the cathode, another chemical reaction occurs, allowing that electrode to accept electrons. This reduction-oxidation process is what distinguishes electrochemical reactions from conventional chemical reactions.
The chemical reactions in batteries involve the flow of electrons from one electrode to another through an external circuit. The flow of electrons provides the electric current, and the charged ions flow through an electrolyte solution in contact with both electrodes. Different electrodes and electrolytes produce different chemical reactions, impacting the battery's performance, energy storage, and voltage.
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Electrolysis
The chemical change that occurs during electrolysis can be described as oxidation or reduction. At the cathode, the change may involve the deposition of a metal, the liberation of hydrogen, or some other chemical reduction process. Meanwhile, at the anode, the change may involve the dissolution of the anode, the liberation of a non-metal, the production of oxygen, or some other chemical oxidation process.
The amount of electrical energy required for electrolysis depends on the specific reaction and conditions. In some cases, such as the electrolysis of steam into hydrogen and oxygen at high temperatures, the process absorbs heat energy from the surroundings, resulting in a higher heating value of the produced hydrogen compared to the electric input.
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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 liquid.
The passage of electricity through gases generally causes chemical changes, and this kind of reaction forms a separate branch of electrochemistry.
When a current is passed between electrodes through an electrolyte, heating and magnetic effects are produced, along with chemical changes. At the negative electrode (cathode), there may be the deposition of a metal, the liberation of hydrogen, or the formation of a basic substance. At the positive electrode (anode), there may be the dissolution of the anode, the liberation of a non-metal, or the production of oxygen and an acidic substance.
