📚 Standard Electrode Potentials and Electrochemical Cells | 标准电极电势与电化学电池
Standard electrode potentials allow chemists to measure how easily a half-cell species gains electrons. This article covers Edexcel A Level Chemistry Topic 14.1 ideas: E⦵ values, the standard hydrogen electrode, electrochemical cells, cell diagrams, E⦵cell calculations, and reaction feasibility.
标准电极电势可以帮助化学家衡量半电池物质获得电子的难易程度。本文涵盖 Edexcel A Level 化学主题 14.1 的核心内容：E⦵ 值、标准氢电极、电化学电池、电池图示、E⦵cell 计算以及反应可行性。
1. Oxidation and Reduction Revisited | 氧化还原反应回顾
Redox chemistry is built on electron transfer. Oxidation is the loss of electrons, and reduction is the gain of electrons. A half-equation shows one of these processes on its own, with the electrons included explicitly.
氧化还原化学建立在电子转移之上。氧化是失去电子，还原是得到电子；半反应式单独表示其中一个过程，并明确写出参与的电子。
For the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), zinc is oxidised to Zn²⁺, while copper(II) ions are reduced to copper metal. The two half-equations are Zn(s) → Zn²⁺(aq) + 2e⁻ and Cu²⁺(aq) + 2e⁻ → Cu(s).
在反应 Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s) 中，锌被氧化为 Zn²⁺，而铜(II)离子被还原为铜金属。两个半反应式分别为 Zn(s) → Zn²⁺(aq) + 2e⁻ 和 Cu²⁺(aq) + 2e⁻ → Cu(s)。
When a half-equation is written with electrons on the left, it shows reduction. Edexcel electrode potential data always lists half-equations as reduction processes: oxidised form + ne⁻ ⇌ reduced form.
当半反应式的电子写在左侧时，它表示还原过程。Edexcel 电极电势数据总是以还原方向列出半反应式：氧化态 + ne⁻ ⇌ 还原态。
2. Defining Standard Electrode Potential E⦵ | 标准电极电势 E⦵ 的定义
The standard electrode potential E⦵ is the electromotive force of a half cell connected to the standard hydrogen electrode, measured under standard conditions. Standard conditions are 298 K, 100 kPa, and 1 mol dm⁻³ solution concentration for aqueous ions.
标准电极电势 E⦵ 是指在标准条件下，将某半电池与标准氢电极连接后测得的电动势。标准条件是 298 K、100 kPa 以及水合离子浓度为 1 mol dm⁻³。
A more negative E⦵ means the reduced form is a stronger reducing agent and the oxidised form is harder to reduce. A more positive E⦵ means the oxidised form is a stronger oxidising agent and is more easily reduced.
E⦵ 越负，说明还原态是更强的还原剂，氧化态更难被还原。E⦵ 越正，说明氧化态是更强的氧化剂，且更容易被还原。
The standard electrode potential is written in the form E⦵(oxidised form/reduced form). For example, E⦵(Zn²⁺/Zn) = -0.76 V and E⦵(Cu²⁺/Cu) = +0.34 V.
标准电极电势写作 E⦵(氧化态/还原态)。例如 E⦵(Zn²⁺/Zn) = -0.76 V，E⦵(Cu²⁺/Cu) = +0.34 V。
3. The Standard Hydrogen Electrode | 标准氢电极
The standard hydrogen electrode is the reference half cell against which all other electrode potentials are measured. It is assigned a value of exactly 0.00 V at all temperatures.
标准氢电极是测量所有其他电极电势时使用的参比半电池。在任何温度下，它都被规定为 0.00 V。
It consists of a platinum electrode immersed in a solution containing 1 mol dm⁻³ H⁺ ions. Hydrogen gas at 100 kPa is bubbled over the platinum surface, and the half-equation is 2H⁺(aq) + 2e⁻ ⇌ H₂(g).
它由一个铂电极浸入含 1 mol dm⁻³ H⁺ 离子的溶液中构成。100 kPa 的氢气在铂电极表面鼓泡，半反应式为 2H⁺(aq) + 2e⁻ ⇌ H₂(g)。
Platinum is used because it is inert, conducts electricity, and provides a surface for the H₂ / H⁺ equilibrium to establish. The surface allows hydrogen molecules to adsorb, dissociate, and release electrons reversibly.
使用铂是因为它惰性、能导电，并且可以为 H₂ / H⁺ 平衡提供反应表面。该表面使氢分子能够可逆地吸附、解离并释放电子。
4. Measuring Standard Electrode Potentials | 测量标准电极电势
To measure the standard electrode potential of a half cell, it is connected to the standard hydrogen electrode through a salt bridge. A high-resistance voltmeter completes the external circuit, so the potential difference is measured without significant current flow.
要测量某半电池的标准电极电势，需将其通过盐桥与标准氢电极相连。高电阻电压表组成外电路，因此在几乎没有电流通过的情况下测量电势差。
The sign of the potential depends on which direction electrons flow in the external circuit. If electrons flow from the metal half cell to the hydrogen electrode, the metal is the negative electrode and its E⦵ is negative.
电势的符号取决于电子在外电路中的流动方向。如果电子从金属半电池流向氢电极，则该金属是负极，其 E⦵ 为负值。
For example, when the Zn²⁺/Zn half cell is connected to the standard hydrogen electrode, electrons flow from zinc to the hydrogen electrode. Therefore E⦵(Zn²⁺/Zn) is -0.76 V. In contrast, the Cu²⁺/Cu half cell pulls electrons from the hydrogen electrode, so E⦵(Cu²⁺/Cu) is +0.34 V.
例如，当 Zn²⁺/Zn 半电池与标准氢电极连接时，电子从锌流向氢电极，因此 E⦵(Zn²⁺/Zn) 为 -0.76 V。相反，Cu²⁺/Cu 半电池会从氢电极吸引电子，因此 E⦵(Cu²⁺/Cu) 为 +0.34 V。
5. Electrochemical Cells and Cell Diagrams | 电化学电池与电池图示
An electrochemical cell consists of two half cells connected by a salt bridge and an external wire. The half cell where oxidation occurs is the negative electrode, while the half cell where reduction occurs is the positive electrode.
电化学电池由两个半电池通过盐桥和外导线连接组成。发生氧化的半电池为负极，发生还原的半电池为正极。
A cell diagram is a shorthand representation of the cell. The vertical line | shows a phase boundary between a solid and an aqueous ion, and a double vertical line || represents the salt bridge.
电池图示是电池的简写表示。单竖线 | 表示固体与水合离子之间的相界面，双竖线 || 表示盐桥。
Zn | Zn²⁺(aq) || Cu²⁺(aq) | Cu
In this cell diagram, zinc metal is oxidised at the left-hand electrode and copper(II) ions are reduced at the right-hand electrode. Electrons travel from zinc to copper in the external circuit.
在这个电池图示中，锌金属在左侧电极被氧化，铜(II)离子在右侧电极被还原。电子在外电路中从锌流向铜。
6. Calculating Standard Cell Potential E⦵cell | 计算标准电池电动势 E⦵cell
The standard cell potential is calculated from the standard electrode potentials of the two half cells. The cell diagram is read as: left-hand half cell is oxidation, right-hand half cell is reduction.
标准电池电动势由两个半电池的标准电极电势计算得出。电池图示的读取规则是：左侧半电池发生氧化，右侧半电池发生还原。
E⦵cell = E⦵(right) − E⦵(left)
For the zinc-copper cell, E⦵cell = +0.34 V − (−0.76 V) = +1.10 V. A positive cell potential shows that the overall reaction is feasible in the direction written.
对于锌-铜电池，E⦵cell = +0.34 V − (−0.76 V) = +1.10 V。正的电池电动势表明所写的总反应方向具有可行性。
| Half-equation | E⦵ / V |
|---|---|
| Zn²⁺(aq) + 2e⁻ ⇌ Zn(s) | -0.76 |
| Fe²⁺(aq) + 2e⁻ ⇌ Fe(s) | -0.44 |
| 2H⁺(aq) + 2e⁻ ⇌ H₂(g) | 0.00 |
| Cu²⁺(aq) + 2e⁻ ⇌ Cu(s) | +0.34 |
| MnO₄⁻(aq) + 8H⁺(aq) + 5e⁻ ⇌ Mn²⁺(aq) + 4H₂O(l) | +1.51 |
The more positive reduction potential is the stronger oxidising agent. Therefore MnO₄⁻ in acidic solution can oxidise Zn, Fe, H₂, and Cu under standard conditions.
还原电势越正，氧化态的氧化性越强。因此酸性条件下的 MnO₄⁻ 可以在标准条件下氧化 Zn、Fe、H₂ 和 Cu。
7. Predicting Reaction Feasibility | 预测反应可行性
An overall redox reaction is thermodynamically feasible if E⦵cell is positive. The half cell with the more positive E⦵ is reduced and the half cell with the more negative E⦵ is oxidised.
如果 E⦵cell 为正值，则整个氧化还原反应在热力学上是可行的。E⦵ 较正的半电池被还原，E⦵ 较负的半电池被氧化。
For example, can acidified dichromate(VI) oxidise Fe²⁺ to Fe³⁺? The relevant half-equations are Fe³⁺ + e⁻ ⇌ Fe²⁺ with E⦵ = +0.77 V and Cr₂O₇²⁻ + 14H⁺ + 6e⁻ ⇌ 2Cr³⁺ + 7H₂O with E⦵ = +1.33 V.
例如，酸性重铬酸根 Cr₂O₇²⁻ 能否氧化 Fe²⁺ 为 Fe³⁺？相关半反应式为 Fe³⁺ + e⁻ ⇌ Fe²⁺，E⦵ = +0.77 V；以及 Cr₂O₇²⁻ + 14H⁺ + 6e⁻ ⇌ 2Cr³⁺ + 7H₂O，E⦵ = +1.33 V。
E⦵cell = E⦵(Cr₂O₇²⁻/Cr³⁺) − E⦵(Fe³⁺/Fe²⁺) = +1.33 V − +0.77 V = +0.56 V. The positive value confirms that dichromate(VI) can oxidise Fe²⁺ under standard acidic conditions.
E⦵cell = E⦵(Cr₂O₇²⁻/Cr³⁺) − E⦵(Fe³⁺/Fe²⁺) = +1.33 V − +0.77 V = +0.56 V。正值确认在标准酸性条件下，重铬酸根可以氧化 Fe²⁺。
8. Limitations of E⦵ Predictions | E⦵ 预测的局限性
E⦵ values apply only under standard conditions. If the temperature changes, the pressure changes, or the ion concentrations change, the actual cell potential will move away from E⦵cell.
E⦵ 值仅适用于标准条件。如果温度、压力或离子浓度发生变化，实际电池电动势就会偏离 E⦵cell。
A positive E⦵cell indicates thermodynamic feasibility, but it does not tell us about the rate of reaction. Some feasible reactions are kinetically very slow, such as the reaction between magnesium and cold water.
E⦵cell 为正只表示热力学可行，并不说明反应速率。某些可行反应在动力学上非常缓慢，例如镁与冷水的反应。
In addition, solid surfaces may become passivated. For instance, aluminium has a negative E⦵(Al³⁺/Al) but resists acid attack because of a protective oxide layer.
此外，固体表面可能会发生钝化。例如，铝的 E⦵(Al³⁺/Al) 为负值，但由于表面有保护性氧化层，铝能抵抗酸的侵蚀。
9. Storage Cells and Fuel Cells | 蓄电池与燃料电池
Storage cells and fuel cells use redox reactions to generate electrical energy. In a storage cell, the chemical reactants are contained within the cell and can be recharged by applying an external current.
蓄电池和燃料电池利用氧化还原反应产生电能。蓄电池的化学物质封装在电池内部，并可通过外加电流进行再充电。
In a hydrogen-oxygen fuel cell, hydrogen is oxidised at the negative electrode and oxygen is reduced at the positive electrode. The overall reaction is 2H₂(g) + O₂(g) → 2H₂O(l).
在氢氧燃料电池中，氢气在负极被氧化，氧气在正极被还原。总反应为 2H₂(g) + O₂(g) → 2H₂O(l)。
Fuel cells are more efficient than internal combustion engines because they convert chemical energy directly into electrical energy. They also produce only water when hydrogen is used, so they do not emit carbon dioxide at the point of use.
燃料电池比内燃机效率更高，因为它们直接将化学能转化为电能。使用氢气时只生成水，因此在使用时不会排放二氧化碳。
10. Exam Tips for Topic 14.1 | 主题 14.1 考试技巧
Always give the standard electrode potential with the correct sign and units. E⦵ values are measured in volts, V, and the sign must be retained when using the formula E⦵cell = E⦵(right) − E⦵(left).
标准电极电势必须写出正确的符号和单位。E⦵ 值的单位是伏特 V，使用公式 E⦵cell = E⦵(
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