How Reduction Potential Influences Chemical Reactions and Cells
What is Reduction Potential?
The electrode potential is called oxidation potential, and the reduction potential is termed as oxidation potential if the oxidation occurs at the electrode. Reduction involves a gain of electrons, and so, the electrode tendency to gain electrons is referred to as its reduction potential.
The potential equilibrium difference of the metal electrode and the solution surrounding it is known as the electrode potential. It is also described as the electrode tendency either to lose or gain electrons.
Reduction Potential Explanation
When a metal piece is immersed in a solution of its own ions, a potential difference is formed at the metal interface and the solution. The potential difference magnitude is a measure of the electrode tendency to undergo either reduction or oxidation or the tendency to either lose or gain the electrons.
The ion and metal represent half cell, and the reaction is the half-reaction. The immersed metal is called an electrode, and the potential occurred because of the reaction at the electrode interface. The solution is known as the electrode potential. Thereby, the electrode potential is described as the tendency of an electrode either to lose or gain electrons. If the reduction occurs at the electrode, it is defined as the reduction potential.
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If the oxidation occurs at the electrode, it is referred to as the oxidation potential.
M → M²⁺ + 2e⁻
As metal ions start depositing on the metal surface and this develops a positive charge on the particular metal rod. Since oxidation is simply a reverse of reduction and thus the reduction potential is obtained from the oxidation potential just by changing the sign.
Generally, for an electrode:
Oxidation potential = – Reduction potential
As an example, in a zinc electrode, the standard oxidation potential can be represented as follows:
E\[^{0}\] (\[\frac{Zn}{Zn^{2+}}\]) = 0.76v
and the standard reduction potential can be given as follows:
E\[^{0}\] (\[\frac{Zn^{2+}}{Zn}\]) = - 0.76v
It is quite common practice to show all the electrode potentials as the reduction potentials.
Very recently, the reduction potential has been adopted by the department of the International Union of Pure and Applied Chemistry (IUPAC) for the electrode potential designation.
When the half-cell reaction is carried out with a temperature of 298K, and the electrode is suspended in one single molar solution concentration, the electrode potential can be defined as the standard electrode potential, and it can be represented by E\[^{0}\]. Moreover, the Standard electrode potential E\[^{0}\] enables one to assess the activity of thermodynamics of different chemical substances. However, there are no other methods available where we can measure its absolute value. The electrode potential of an electrode can be measured with respect to the standard hydrogen electrode.
The electrode potential of an electrode completely depends upon the concentration of ions in a solution in contact with the metal. In simple words, the oxidation potential of an electrode is inversely proportional to the ion concentration, whereas the reduction potential is directly proportional to the ion concentration.
Half Cells
As a cell, a battery has two half-cells separated with an electrolyte. The electrodes are required to connect the half cells to the external circuit. Every electrode can act as part of a redox couple, but none of these has to be.
The standard conditions for the hydrogen half-cell are the concentration of hydrogen [H⁺(AQ)], the pressure of hydrogen gas is given as 105Pa with a temperature of 298K.
The standard hydrogen half-cell can be used as a reference half-cell, whereas all the other half-cells are measured against it. An electrode potential list has been generated relative to the half-cell of standard hydrogen. The half-reaction in this half cell is given as follows:
2H⁺(aq) + 2e⁻ ⇌ H₂(g)
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Electrodes potentials differ with the temperature, and thus, a standard temperature can be defined. This is given as 298K. By altering any ion concentration appearing in the half-reactions also affects the voltages, and thus, a standard concentration of 1.00 mol dm-3 can be chosen. Standard pressure is given as 105Pa.
The potential of a standard hydrogen half-cell can be described as 0.0V, which is a value chosen for convenience.
The half-cell’s standard electrode potential E\[^{0}\] can be defined as the potential difference between the half-cell and the standard hydrogen half-cell.
E\[^{0}\] values contain a sign based on whether the half-cell is at either a higher or lower positive potential compared to the standard hydrogen half-cell. The measurements are created at 298K with a metal dipping into a 1.00 mol dm-3 solution of the metal’s salt.
Effects of Reduction Potential
Generally, very late transition metal ions at the right end of the transition metal chain, including silver, copper, gold, contain a high potential for reduction. If the normal reduction potential of the lithium is more negative, then the oxidation potential of the lithium-ion is very positive.
FAQs on Reduction Potential Explained: Definition, Examples & Importance
1. What is the basic definition of reduction potential in chemistry?
Reduction potential is a measure of the tendency of a chemical species to gain electrons and thereby be reduced. It is measured in volts (V) and indicates how likely a substance is to act as an oxidizing agent. A higher reduction potential means a greater tendency to accept electrons.
2. How does reduction potential differ from oxidation potential?
Reduction potential and oxidation potential represent opposite processes. While reduction potential measures the tendency to gain electrons, oxidation potential measures the tendency to lose electrons. They have the same magnitude but opposite signs for the same chemical species. For any electrode, the oxidation potential is the negative of its reduction potential (E°oxidation = -E°reduction).
3. What does a positive standard reduction potential (E°) signify?
A positive standard reduction potential (E°) indicates that the chemical species has a stronger tendency to be reduced than hydrogen ions (H⁺) under standard conditions. This means it is a good oxidizing agent because it readily accepts electrons. For example, Cu²⁺ has a positive E° (+0.34 V), so it is easily reduced to Cu.
4. What is the implication of a negative standard reduction potential (E°)?
A negative standard reduction potential (E°) implies that the chemical species has a weaker tendency to be reduced compared to hydrogen ions (H⁺). Instead, it is more likely to be oxidized. Such a species is a good reducing agent because it readily donates electrons. For instance, Zinc (Zn) has a negative E° (-0.76 V), indicating it prefers to be oxidized to Zn²⁺.
5. Why is the Standard Hydrogen Electrode (SHE) essential for measuring reduction potential?
It is impossible to measure the absolute potential of a single half-cell. Therefore, a reference electrode is needed to measure the relative potential difference. The Standard Hydrogen Electrode (SHE) is the universal reference, and its reduction potential is arbitrarily assigned a value of exactly 0.00 volts under standard conditions (298 K, 1 M concentration, 1 bar pressure). All other standard reduction potentials are measured relative to the SHE.
6. How is the overall cell potential (E°cell) calculated using standard reduction potentials?
The standard potential of an electrochemical cell (E°cell) is calculated by subtracting the standard reduction potential of the anode from the standard reduction potential of the cathode. The formula is:
E°cell = E°cathode (reduction half-reaction) - E°anode (oxidation half-reaction)
The cathode is where reduction occurs, and the anode is where oxidation occurs.
7. What is an example of an element with a very high reduction potential and what does it mean?
Fluorine (F₂) has the highest standard reduction potential (+2.87 V) in the electrochemical series. This extremely high positive value means that fluorine has a tremendous tendency to gain electrons and be reduced to fluoride ions (F⁻). Consequently, fluorine gas is the strongest oxidizing agent known.
8. How does the value of reduction potential help predict if a redox reaction will occur spontaneously?
The standard reduction potential is crucial for predicting the spontaneity of a redox reaction. A reaction is considered spontaneous if its calculated standard cell potential (E°cell) is positive. To determine this, you follow these steps:
Identify the two half-reactions (oxidation and reduction).
Use the formula E°cell = E°cathode - E°anode.
If E°cell > 0, the reaction proceeds spontaneously as written.
If E°cell < 0, the reaction is non-spontaneous in the forward direction but spontaneous in the reverse direction.
