IB & CIE Chemistry: Electrochemistry Key Revision Points | IB CIE 化学：电化学考点精讲

📚 IB & CIE Chemistry: Electrochemistry Key Revision Points | IB CIE 化学：电化学考点精讲

Electrochemistry is a high‑yield topic in both IB and CIE Chemistry, linking redox reactions, thermodynamic spontaneity, and practical applications like batteries, electrolysis, and corrosion. This revision guide breaks down the core concepts, key equations, and exam‑savvy tips you need to master – with paired English‑Chinese explanations for every point.

电化学是 IB 和 CIE 化学中的高频考点，它串联了氧化还原反应、热力学自发性和电池、电解、腐蚀等实际应用。这篇精讲梳理了核心概念、关键公式和应试技巧，每个要点都提供中英对照讲解，帮助你彻底掌握。

1. Redox Fundamentals | 氧化还原基础

Redox (reduction‑oxidation) reactions involve the transfer of electrons. Oxidation is the loss of electrons (increase in oxidation state); reduction is the gain of electrons (decrease in oxidation state). The substance that gets reduced is the oxidising agent, and the one that gets oxidised is the reducing agent.

氧化还原反应涉及电子转移。氧化是指失去电子（氧化数升高），还原是指得到电子（氧化数降低）。被还原的物质是氧化剂，被氧化的物质是还原剂。

A handy mnemonic is OIL RIG: Oxidation Is Loss, Reduction Is Gain. Always assign oxidation states using rules such as oxygen = –2 (except in peroxides), hydrogen = +1 (except in metal hydrides), and the sum equals the overall charge.

记忆口诀 OIL RIG：氧化失电子，还原得电子。要熟记氧化数规则：氧一般为 –2（过氧化物除外），氢一般为 +1（金属氢化物除外），总和等于粒子所带电荷。

Half‑equations show electron transfer explicitly. For example, Zn → Zn²⁺ + 2e⁻ (oxidation) and Cu²⁺ + 2e⁻ → Cu (reduction). In acidic solution, balance O with H₂O and H with H⁺; in basic solution, add OH⁻ after balancing as if acidic.

半反应方程明确表示电子得失。例如 Zn → Zn²⁺ + 2e⁻（氧化），Cu²⁺ + 2e⁻ → Cu（还原）。在酸性条件下，用 H₂O 平衡 O，用 H⁺ 平衡 H；碱性条件下先按酸性配平，再添加 OH⁻ 中和 H⁺。

2. Electrochemical Cells: Galvanic vs Electrolytic | 原电池与电解池

A galvanic (voltaic) cell converts chemical energy into electrical energy through a spontaneous redox reaction. It consists of two half‑cells connected by a salt bridge and an external circuit. Oxidation occurs at the anode (negative in galvanic cells), reduction at the cathode (positive). Electrons flow from anode to cathode through the external wire.

原电池通过自发的氧化还原反应将化学能转化为电能。它由两个半电池、盐桥和外电路组成。氧化发生在阳极（原电池中为负极），还原发生在阴极（正极）。电子经外导线从阳极流向阴极。

An electrolytic cell uses an external power source to drive a non‑spontaneous reaction. Here the anode is positive and the cathode is negative, but oxidation still occurs at the anode and reduction at the cathode. The salt bridge is replaced by the electrolyte itself, and the electrodes may be inert (graphite, platinum).

电解池用外电源驱动非自发反应。此时阳极为正极，阴极为负极，但阳极依旧发生氧化，阴极发生还原。盐桥被同一电解液取代，电极常用惰性材料（石墨、铂）。

In both cells, the total cell reaction is obtained by combining the two half‑equations so that electrons cancel. Never change the reduction potential values when multiplying half‑equations to balance electrons.

两种电池的总反应都是将两个半反应相加使电子抵消。为配平电子而乘以整数时，标准电极电势的数值不变。

3. Standard Hydrogen Electrode & Cell Potentials | 标准氢电极与电极电势

The standard hydrogen electrode (SHE) is assigned a potential of exactly 0.00 V under standard conditions (298 K, 1 atm H₂, 1 mol dm⁻³ H⁺). All other standard electrode potentials (E°) are measured relative to the SHE, connected via a salt bridge. By convention, E° values refer to the reduction half‑reaction.

标准氢电极（SHE）在标准条件（298 K，1 atm H₂，1 mol dm⁻³ H⁺）下电势恰好为 0.00 V。所有其他标准电极电势 E° 都是相对于 SHE 通过盐桥测量。按惯例，E° 值对应的是还原半反应。

The standard cell potential is calculated as E°(cell) = E°(cathode) – E°(anode), where both E° are reduction potentials. A positive E°(cell) indicates a spontaneous reaction under standard conditions.

标准电池电动势的计算公式为 E°(cell) = E°(cathode) – E°(anode)，其中两个 E° 均为还原电势。若 E°(cell) 为正，表示该反应在标准条件下自发进行。

E°(cell) = E°(cathode) − E°(anode)

For example, with Zn²⁺/Zn (–0.76 V) and Cu²⁺/Cu (+0.34 V), the Cu half‑cell has the higher reduction potential and acts as the cathode: E°(cell) = 0.34 – (–0.76) = +1.10 V.

例如 Zn²⁺/Zn (–0.76 V) 与 Cu²⁺/Cu (+0.34 V)，铜半电池的还原电势更高，作阴极：E°(cell) = 0.34 – (–0.76) = +1.10 V。

4. Spontaneity, Gibbs Free Energy & Equilibrium | 自发性、吉布斯自由能与平衡常数

The link between cell potential and thermodynamics is given by ΔG° = –nFE°(cell), where n is the number of moles of electrons transferred and F is the Faraday constant ( ≈ 96 500 C mol⁻¹). A negative ΔG° matches a positive E°(cell).

电池电势与热力学的桥梁公式为 ΔG° = –nFE°(cell)，n 为转移电子的物质的量，F 为法拉第常数（≈96 500 C mol⁻¹）。ΔG° 为负对应 E°(cell) 为正。

ΔG° = −nFE°(cell)

Moreover, ΔG° = –RT ln K, so we can find the equilibrium constant K from the standard cell potential at 298 K: ln K = nFE°(cell) / (RT). A large K (K > 1) arises when E°(cell) is significantly positive.

又因 ΔG° = –RT ln K，可在 298 K 下由标准电池电势求 K：ln K = nFE°(cell) / (RT)。当 E°(cell) 明显为正时，K 值很大（K > 1）。

This relationship allows us to compare the relative strengths of oxidising and reducing agents. The more positive the standard reduction potential, the stronger the oxidising agent.

由此可比较氧化剂和还原剂的相对强弱：标准还原电势越正，该物质的氧化性越强。

5. The Nernst Equation | 能斯特方程

Under non‑standard conditions (concentrations not 1 mol dm⁻³, pressures not 1 atm), the cell potential E deviates from E°. The Nernst equation for a half‑cell at 298 K is:

在非标准条件下（浓度不为 1 mol dm⁻³，压强不为 1 atm），电池电势 E 偏离 E°。298 K 下半反应的能斯特方程为：

E = E° + (0.0592 / n) × log₁₀([oxidised form] / [reduced form])

Where n is the number of electrons in the half‑reaction. For a full cell, E = E°(cell) – (0.0592 / n) log₁₀ Q, with Q being the reaction quotient.

n 为半反应中的电子数。对于整个电池，E = E°(cell) – (0.0592 / n) log₁₀ Q，Q 为反应商。

E = E° − (0.0592 / n) log₁₀ Q

Notice that when Q = K (the cell has reached equilibrium), ΔG = 0 and E = 0. This is consistent with a “dead” battery.

注意到当 Q = K（电池达到平衡）时，ΔG=0 且 E=0。这与电池 “耗尽” 一致。

6. Using the Electrochemical Series | 电化序的应用

The electrochemical series lists half‑reactions in order of decreasing standard reduction potential. It helps to predict whether a metal will displace another from solution, or whether a redox reaction is feasible. For instance, a metal higher up in the series (more negative E°) will displace a lower one from its salt solution.

电化序按标准还原电势从大到小排列半反应。它可用于预测金属能否从溶液中置换出另一种金属，或某一氧化还原反应是否可行。电势更负的金属能将电势更正的金属从其盐溶液中置换出来。

Also, species with very positive E° (e.g., F₂/F⁻, +2.87 V) are strong oxidising agents; those with very negative E° (e.g., Li⁺/Li, –3.04 V) are strong reducing agents.

同时，E° 很正的物质（如 F₂/F⁻，+2.87 V）是强氧化剂；E° 很负的物质（如 Li⁺/Li，–3.04 V）是强还原剂。

Beware: kinetic factors may prevent a thermodynamically feasible reaction. For example, Al has a very negative E°, yet it does not react vigorously with water because of its protective oxide layer.

注意：动力学因素可能阻止热力学上可行的反应。比如 Al 的 E° 很负，但由于表面致密氧化膜，它并不与水剧烈反应。

7. Electrolytic Cells & Faraday’s Laws | 电解池与法拉第定律

Electrolysis is the decomposition of an electrolyte by an electric current. At the cathode, reduction happens; at the anode, oxidation. In aqueous solutions, water can be oxidised to O₂ or reduced to H₂, competing with the solute. The product depends on the relative E° values and overpotential effects.

电解是利用电流使电解质分解的过程。阴极发生还原，阳极发生氧化。在水溶液中，水本身可被氧化为 O₂ 或还原为 H₂，与溶质竞争放电。产物取决于相对标准电势和过电位效应。

Faraday’s laws quantify the mass of substance produced: m = (M I t) / (n F), where m is mass (g), M is molar mass (g mol⁻¹), I is current (A), t is time (s), n is electrons per ion, and F = 96 500 C mol⁻¹.

法拉第定律定量计算电解产物质量：m = (M I t) / (n F)，m 为质量 (g)，M 为摩尔质量 (g mol⁻¹)，I 为电流 (A)，t 为时间 (s)，n 为每个离子对应的电子数，F = 96 500 C mol⁻¹。

Q = I t and m = (M Q) / (n F)

Common calculations ask for the volume of gas liberated or the thickness of a plated layer; always convert to the amount of electrons first.

常见计算要求求出气体的体积或电镀层的厚度，一律先从电子物质的量入手。

8. Applications: Electroplating & Aluminium Extraction | 应用：电镀与铝的冶炼

Electroplating uses an electrolytic cell to coat a metal object with a thin layer of another metal. The object to be plated is made the cathode, the plating metal the anode (often an inert anode is used with a metal salt solution). This process improves corrosion resistance and appearance.

电镀利用电解池在金属物体表面覆盖一层其他金属。待镀物件作阴极，镀层金属作阳极（常用惰性阳极配合金属盐溶液）。电镀可增强耐腐蚀性和改善外观。

Aluminium is extracted by the Hall‑Héroult process, electrolysis of purified Al₂O₃ dissolved in molten cryolite (Na₃AlF₆) at about 950 °C. The anode is graphite, which is consumed by the oxygen produced. The overall reaction is 2Al₂O₃ → 4Al + 3O₂. The high energy cost makes recycling aluminium crucial.

铝的冶炼采用 Hall‑Héroult 法，将纯化的 Al₂O₃ 溶于熔融冰晶石 (Na₃AlF₆) 于约 950 °C 电解。阳极为石墨，被生成的氧消耗。总反应为 2Al₂O₃ → 4Al + 3O₂。高能耗使得铝的回收至关重要。

9. Types of Cells & Batteries | 电池类型

Primary cells (e.g., zinc‑carbon, alkaline) are not rechargeable; the reaction is irreversible. Secondary cells (e.g., lead‑acid, lithium‑ion) allow the cell reaction to be reversed during recharging. Fuel cells convert chemical energy directly into electricity with fuel and oxidant supplied continuously.

一次电池（如锌‑碳、碱性电池）不可充电，反应不可逆。二次电池（如铅酸、锂离子电池）可通过充电使反应逆转。燃料电池将燃料和氧化剂持续输入的化学能直接转化为电能。

Hydrogen‑oxygen fuel cells produce water as the only product, making them environmentally friendly. The half‑reactions in alkaline medium are: H₂ + 2OH⁻ → 2H₂O + 2e⁻ (anode); O₂ + 2H₂O + 4e⁻ → 4OH⁻ (cathode). In acidic medium, water is formed at the cathode.

氢氧燃料电池的唯一产物是水，因此对环境友好。在碱性介质中的半反应为：H₂ + 2OH⁻ → 2H₂O + 2e⁻（阳极）；O₂ + 2H₂O + 4e⁻ → 4OH⁻（阴极）。在酸性介质中，水在阴极生成。

10. Corrosion and Prevention | 腐蚀与防护

Rusting of iron requires oxygen and water; it is an electrochemical process where iron acts as the anode (Fe → Fe²⁺ + 2e⁻) and oxygen is reduced on the cathode surface. The overall rust is hydrated iron(III) oxide.

铁生锈需要氧和水；这是一个电化学过程，铁作为阳极（Fe → Fe²⁺ + 2e⁻），氧在阴极表面被还原。总锈蚀产物是水合氧化铁(III)。

Prevention methods include: barrier protection (paint, grease, plastic coating), galvanising (coating with zinc, which corrodes sacrificially because Zn has a more negative E° than Fe), and cathodic protection (connecting to a more reactive metal, e.g., magnesium, which acts as a sacrificial anode).

防护方法有：隔离保护（涂漆、涂油、包塑料）、镀锌（锌比铁电势更负，优先腐蚀，即牺牲保护）、以及阴极保护（连接更活泼的金属如镁作为牺牲阳极）。

11. Common Exam Pitfalls | 常见失分点

Sign conventions: When using E°(cell) = E°(cathode) – E°(anode), do not swap signs of reduction potentials. The anode is where oxidation occurs, but its potential is still taken from the reduction table.

符号惯例： 用 E°(cell) = E°(cathode) – E°(anode) 时，不要随意改变还原电势的正负号。阳极虽发生氧化，但仍使用还原电势表中的数值。
Stoichiometry and Faraday’s law: Ensure the value of n matches the electrons in the balanced half‑equation, not the overall equation automatically. Many students misuse n for full reaction.

法拉第定律的计量数： 确保 n 与配平的半反应电子数一致，而非直接取用时用总反应的电子数。这是常见错误。
Electrode polarity in different cells: In a galvanic cell, the anode is negative; in an electrolytic cell, the anode is positive. Remember that oxidation always occurs at the anode.

不同电池的电极极性： 原电池中阳极为负极，电解池中阳极为正极。牢记氧化总在阳极发生，极性因电池类型而异。
Nernst equation units: log₁₀ Q uses concentration in mol dm⁻³ and partial pressure in atm. For heterogeneous reactions, pure solids/liquids are omitted. Water is often omitted in dilute solutions.

能斯特方程的浓度项： Q 中浓度单位为 mol dm⁻³，分压单位为 atm。对于多相反应，纯固/液体不写入，稀溶液中的水常被忽略。

12. Summary Checklist | 总结清单

In your revision, ensure you can: calculate E°(cell) correctly; link ΔG°, K and E°; apply the Nernst equation; distinguish galvanic and electrolytic cells; use Faraday’s laws quantitatively; explain corrosion and its prevention; and recall key examples like the hydrogen fuel cell and aluminium extraction. Electrochemistry blends theory with calculation – practise with past‑paper questions to lock in your skills. Good luck!

复习时要确保你能：正确计算 E°(cell)；关联 ΔG°、K 与 E°；应用能斯特方程；区分原电池与电解池；定量使用法拉第定律；解释腐蚀及其防护；并记住氢燃料电池与铝冶炼等典型案例。电化学融合理论与计算，用真题练手能固化解题技能。祝你成功！

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IB & CIE Chemistry: Electrochemistry Key Revision Points | IB CIE 化学：电化学 考点精讲