Beatrice Lang
The electric potential between electrodes is a result of the difference in their individual potentials. This difference is measured in volts, with 1V=1J/C. The standard electrode potential of an electrode can be measured by pairing it with the standard hydrogen electrode (SHE) and measuring the cell potential of the resulting galvanic cell. The standard hydrogen electrode is defined to have a potential of 0V. The electrode with a higher electric potential is the one that is more likely to be reduced, and the one with a lower electric potential is the one that is more likely to be oxidised.
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What You'll Learn
The standard electrode potential
The overall cell potential (Ecell) of an electrochemical cell is the sum of the individual potentials of the electrodes. It can be calculated by subtracting the standard electrode potential of the anode from that of the cathode. This cell potential represents the voltage difference between the two half-cells and is measured using a voltmeter. While the overall cell potential can be determined, it is challenging to measure the potential of a single electrode in isolation.
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The potential of a half-reaction
A half-reaction is either the oxidation or reduction reaction component of a redox reaction. A half-reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. The concept of half-reactions is often used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery.
The standard electrode potential of an electrode can be measured by pairing it with the Standard Hydrogen Electrode (SHE) and measuring the cell potential of the resulting galvanic cell. The oxidation potential of an electrode is the negative of its reduction potential. The standard electrode potential of an electrode is described by its standard reduction potential. The standard reduction potential of a particular half-reaction will have a sign—negative or positive. If the value is positive, then that is how much electricity the half-reaction will contribute to a full galvanic cell. However, if the value is negative, then its magnitude is how much voltage you need to supply to trigger the half-reaction on its own.
The potential of an electrode is known as the potential of a cell consisting of the electrode concerned acting as a cathode and the SHE acting as an anode. The cathode is always reduced, and the anode is oxidized. The standard reduction potential of a half-reaction is measured for the reduction form of the half-reaction and is denoted by \(E^{0}_{red}\). The "red" stands for reduction. The standard reduction potential of an electrode is the potential for the electrode to gain electrons. The higher the standard reduction potential, the better the oxidizing agent.
The standard electrode potential of a cell (Ecell) is measured in voltage (V), which allows us to give a certain value to the cell potential. An electrochemical cell is comprised of two half-cells. In one half-cell, the oxidation of a metal electrode occurs, and in the other half-cell, the reduction of metal ions in solution occurs. The half-cell essentially consists of a metal electrode of a certain metal submerged in an aqueous solution of the same metal ions. The electrode is connected to the other half-cell, which contains an electrode of some metal submerged in an aqueous solution of subsequent metal ions. The first half cell, in this case, will be marked as the anode.
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The potential difference between two half-cells
An electrochemical cell is made up of two half-cells. One half-cell undergoes oxidation, where a metal electrode is oxidized, and electrons are lost, leaving the substance positively charged. The other half-cell undergoes reduction, where metal ions in solution are reduced, and electrons are gained, leaving the substance negatively charged.
The potential difference is caused by the ability of electrons to flow from one half-cell to the other. The electrode in one half-cell has a higher potential to be oxidized, while the electrode in the other half-cell has a lower potential to be oxidized. This potential difference drives the redox reactions in the electrochemical cell. The anode is the electrode with a higher potential to be oxidized, while the cathode is the electrode with a lower potential to be oxidized.
The individual potential of a half-cell cannot be accurately measured in isolation. Instead, the standard electrode potential of an electrode is determined by pairing it with the Standard Hydrogen Electrode (SHE) and measuring the resulting cell potential. The SHE is a platinum electrode immersed in an acidic solution with a concentration of 1 molar hydrogen ions and hydrogen gas at 1 atmosphere pressure.
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The oxidation and reduction half-reactions
The concept of half-reactions is fundamental to understanding oxidation and reduction processes in electrochemistry. A half-reaction is either the oxidation or reduction component of a redox reaction, focusing on the loss or gain of electrons, respectively. These half-reactions can be physically separated in electrochemical cells, with electrons flowing through a connecting wire.
In an electrochemical cell, one half-cell undergoes oxidation, where the metal electrode loses electrons and joins the metal ions in the aqueous solution. This half-cell is the anode, which has a higher potential to be oxidized. The other half-cell undergoes reduction, where metal ions in solution gain electrons. This half-cell is the cathode, which has a higher potential to be reduced. The electrons flow from the anode to the cathode, and this movement is measured as voltage.
To illustrate this with an example, consider a Galvanic cell with a piece of zinc submerged in a solution of zinc sulfate and a piece of copper submerged in a solution of copper(II) sulfate. At the Zn anode, oxidation occurs, and zinc loses electrons. This is the oxidation half-reaction. At the Cu cathode, reduction takes place, and electrons are accepted. This is the reduction half-reaction.
In summary, the oxidation and reduction half-reactions are integral components of redox reactions, occurring at the anode and cathode, respectively. They involve the loss and gain of electrons, and their separation helps in understanding the underlying chemistry, especially in electrochemical cells.
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The potential of a single electrode
The potential of an electrode is influenced by the concentration of metal ions and temperature. The potential of an electrode is also known as the potential of a cell consisting of the electrode concerned acting as a cathode and a standard hydrogen electrode (SHE) acting as an anode. The SHE is defined to have a potential of zero volts. The standard electrode potential of an electrode can be measured by pairing it with the SHE and measuring the cell potential of the resulting galvanic cell. The standard electrode potential of an electrode is described by its standard reduction potential. The oxidation potential of an electrode is the negative of its reduction potential. The standard reduction potential is positive for good oxidizing agents and negative for good reducing agents.
The potential of a cell assembled from two electrodes can be determined from the two individual electrode potentials. The cell potential is measured in voltage (V) and allows us to give a certain value to the cell potential. An electrochemical cell is made up of two half-cells. In one half-cell, the oxidation of a metal electrode occurs, and in the other, the reduction of metal ions in solution occurs. The half-cell consists of a metal electrode submerged in an aqueous solution of the same metal ions. The electrode is connected to the other half-cell, which contains an electrode of some metal submerged in an aqueous solution of subsequent metal ions. The first half-cell is marked as the anode, where the metal atoms in the electrode become oxidized and join the other metal ions in the aqueous solution.
The potential that arises between the anode and cathode of an electrochemical cell is due to the difference in the individual potentials of each electrode (dipped in their respective electrolytes). The cell potential can be measured with a voltmeter. The voltmeter reads the transfer of electrons from the anode to the cathode in joules per coulomb.
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Frequently asked questions
An electrode is a conductor through which electricity enters or leaves an electrical device.
Electrode potential is the voltage of a galvanic cell built from a standard reference electrode and another electrode to be characterized.
The standard electrode potential is a conventional instance of this concept whose reference electrode is the standard hydrogen electrode (SHE), defined to have a potential of zero volts.
The anode has a higher potential to become oxidized, and the cathode has a higher potential to become reduced.
The standard electrode potential of an electrode can be measured by pairing it with the SHE and measuring the cell potential of the resulting galvanic cell.
