IGCSE Chemistry: Electrochemistry Essentials | IGCSE 化学：电化学 考点精讲

📚 IGCSE Chemistry: Electrochemistry Essentials | IGCSE 化学：电化学 考点精讲

Electrochemistry bridges electrical energy and chemical reactions, forming a core part of the IGCSE Chemistry syllabus. It encompasses two key processes: electrolysis, where electricity drives a non-spontaneous chemical change, and electrochemical cells, where spontaneous chemical reactions generate electricity. Understanding the principles, predicting products, and linking theory to real-world applications are essential skills for exam success.

电化学将电能与化学反应联系起来，是IGCSE化学大纲的核心组成部分。它涵盖两个关键过程：电解（利用电能驱动非自发的化学变化）和化学电池（利用自发的化学反应产生电能）。掌握其原理、预测产物并将理论与实际应用相联系，是考试成功的关键技能。

1. What is Electrochemistry? | 电化学简介

Electrochemistry studies the interconversion between electrical energy and chemical energy. It splits into electrolytic cells, where an external power source forces redox reactions, and galvanic cells (voltaic cells), where redox reactions produce an electric current. In IGCSE, you will explore both types, focusing on predicting electrode products and describing simple cells.

电化学研究电能与化学能之间的相互转化。它分为电解池（外部电源强制发生氧化还原反应）和原电池（氧化还原反应自发产生电流）。在IGCSE中，你将探讨这两种类型，重点在于预测电极产物和描述简单电池。

2. Electrolytes and Non-Electrolytes | 电解质与非电解质

An electrolyte is a substance that conducts electricity when molten or dissolved in water because it contains mobile ions. Examples include molten lead(II) bromide, aqueous sodium chloride, and acids. A non-electrolyte does not dissociate into ions; its particles have no net charge or are not free to move, so it cannot conduct. Solid ionic compounds, covalent liquids (like pure water), and sugar solutions are typical non-electrolytes.

电解质是在熔融或水溶液中能导电的物质，因为它含有可自由移动的离子。例子包括熔融溴化铅、氯化钠水溶液和酸类。非电解质不会解离成离子，其粒子没有净电荷或不能自由移动，因此不导电。固体离子化合物、共价液体（如纯水）和糖溶液都是典型的非电解质。

3. Basic Setup of an Electrolytic Cell | 电解池的基本组成

An electrolytic cell consists of a direct current (d.c.) power supply, two electrodes dipped in an electrolyte, and connecting wires. The electrode connected to the positive terminal is the anode (site of oxidation), and the electrode connected to the negative terminal is the cathode (site of reduction). Inert electrodes (graphite or platinum) do not react, while active electrodes (e.g., copper) can take part in the reaction.

电解池由直流电源、浸在电解质中的两个电极以及导线构成。连接电源正极的是阳极（发生氧化反应），连接负极的是阴极（发生还原反应）。惰性电极（石墨或铂）不参与反应，而活性电极（如铜）可能会参与电极过程。

During electrolysis, cations (positive ions) migrate to the cathode and gain electrons. Anions (negative ions) migrate to the anode and lose electrons. This movement of ions completes the circuit and allows reduction at the cathode and oxidation at the anode to occur simultaneously.

电解过程中，阳离子移向阴极并得到电子；阴离子移向阳极并失去电子。离子的这种移动接通了回路，使阴极的还原和阳极的氧化得以同时发生。

4. Discharge Series of Ions | 离子的放电顺序

At the cathode, metal cations and H⁺ from water compete for electrons. The ion that is easier to reduce (lower in the reactivity series) is discharged preferentially. Thus, Cu²⁺ (+0.34 V) is reduced before Zn²⁺, and H⁺ is reduced before very reactive metals such as K⁺, Na⁺, Ca²⁺, Mg²⁺ or Al³⁺. For these reactive metals, H⁺ from water will be discharged, producing hydrogen gas.

在阴极，金属阳离子和水中的 H⁺ 竞争电子。越容易被还原的离子（在金属活动性顺序中位置越低）越优先放电。因此 Cu²⁺ 会先于 Zn²⁺ 被还原，而 H⁺ 则优先于 K⁺、Na⁺、Ca²⁺、Mg²⁺ 或 Al³⁺ 等极活泼金属离子放电。对这些活泼金属，水中的 H⁺ 会放电产生氢气。

At an inert anode, the anion discharge order commonly encountered in IGCSE is: OH⁻ > I⁻ > Br⁻ > Cl⁻ > SO₄²⁻ / NO₃⁻. Sulfate and nitrate ions are very stable and are generally not discharged in aqueous solutions. Halide ion concentration can influence products; in concentrated NaCl(aq), Cl⁻ may be discharged instead of OH⁻, giving chlorine gas.

在惰性阳极上，IGCSE 阶段常见的阴离子放电顺序为：OH⁻ > I⁻ > Br⁻ > Cl⁻ > SO₄²⁻ / NO₃⁻。硫酸根和硝酸根离子很稳定，在水溶液中通常不放电。卤离子浓度会影响产物；在浓氯化钠溶液中，Cl⁻ 可能优先于 OH⁻ 放电，生成氯气。

上表总结了阳离子和阴离子在惰性电极上的放电难易顺序。注意 H⁺ 的位置：它比 Zn² ⁺ 难放电，但比 Na⁺ 等更容易放电。

5. Electrolysis of Molten Ionic Compounds | 熔融离子化合物的电解

When a molten ionic compound is electrolysed, the only ions present are those from the compound. For example, molten lead(II) bromide, PbBr₂, contains Pb²⁺ and Br⁻ ions. At the cathode: Pb²⁺ + 2e⁻ → Pb (grey lead metal deposits). At the anode: 2Br⁻ → Br₂ + 2e⁻ (red-brown bromine gas released).

当电解熔融离子化合物时，存在的离子仅来自该化合物。例如，熔融溴化铅 PbBr₂ 中含有 Pb²⁺ 和 Br⁻。阴极：Pb²⁺ + 2e⁻ → Pb（析出灰色铅）；阳极：2Br⁻ → Br₂ + 2e⁻（释放红棕色溴蒸气）。

Pb²⁺ + 2e⁻ → Pb   |   2Br⁻ → Br₂ + 2e⁻

In molten aluminium oxide, Al₂O₃, the ions are Al³⁺ and O²⁻. The cathode reaction is Al³⁺ + 3e⁻ → Al, and the anode reaction is 2O²⁻ → O₂ + 4e⁻. This process is used in aluminium extraction, but with added cryolite to lower the melting point.Published by TutorHao | IGCSE Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）