📚 Electrolysis: Principles, Predictions and Industrial Processes | 电解：原理、预测与工业过程
Electrolysis is the chemical decomposition of an ionic compound using direct current electricity. It is a key topic in Cambridge A-Level Chemistry, bridging the gap between electricity and chemical change. Understanding electrolysis requires a firm grasp of redox processes, ion migration, and the electrochemical series.
电解是利用直流电使离子化合物发生化学分解的过程，这是剑桥A-Level化学的核心主题，连接了电学与化学变化。要理解电解，必须扎实掌握氧化还原过程、离子迁移以及电化学序。
1. What is Electrolysis? | 什么是电解？
Electrolysis involves passing an electric current through a molten or dissolved ionic compound, causing it to decompose into its constituent elements. The process is non-spontaneous and requires an external source of electrical energy. The substance that conducts electricity and decomposes is called the electrolyte.
电解是通过熔融或溶解的离子化合物通入电流，使其分解为组成元素的过程。该过程非自发，需要外部电能。能导电并分解的物质称为电解质。
During electrolysis, positive ions (cations) migrate to the negative electrode (cathode) and negative ions (anions) move to the positive electrode (anode), where they undergo reduction and oxidation respectively. This movement of ions completes the electrical circuit inside the cell.
电解过程中，阳离子向负极（阴极）移动，阴离子向正极（阳极）移动，分别在电极上发生还原和氧化反应。离子的这种移动形成了电池内部的回路。
2. Comparing Electrolytic and Galvanic Cells | 比较电解池与伏打电池
An electrolytic cell converts electrical energy into chemical energy, whereas a galvanic (voltaic) cell converts chemical energy into electrical energy. In an electrolytic cell, the cathode is negative and the anode is positive, opposite to the galvanic cell where the cathode is positive and anode is negative.
电解池将电能转化为化学能，而伏打（原电池）将化学能转化为电能。在电解池中，阴极为负极，阳极为正极，与伏打电池（阴正阳负）正好相反。
Both types of cells involve redox reactions, but electrolysis forces non-spontaneous reactions to occur by applying an external voltage greater than the cell potential of the reverse spontaneous reaction. The external power source pushes electrons into the cathode and pulls them from the anode.
两类电池都涉及氧化还原反应，但电解通过施加比逆反应电池电势更高的外部电压，迫使非自发反应发生。外部电源将电子推入阴极，并从阳极拉出电子。
3. The Electrolytic Cell: Electrolyte, Electrodes, and Current | 电解池：电解质、电极和电流
The electrolyte must contain mobile ions, either as a molten salt or an aqueous solution. Electrodes are usually inert (graphite or platinum) or can be reactive (e.g., copper electrodes in purification). Direct current drives migration: cations to the cathode for reduction, anions to the anode for oxidation.
电解质必须含有可自由移动的离子，可以是熔融盐或水溶液。电极通常为惰性材料（石墨或铂），也可以是活性电极（如铜精炼中的铜电极）。直流电驱动离子迁移：阳离子趋向阴极发生还原，阴离子趋向阳极发生氧化。
The circuit is completed by the movement of electrons in the external wire and ions in the electrolyte. Electrodes must not touch each other, and a power source maintains the potential difference.
外电路电子流动与电解质中离子移动共同构成回路。两电极不可接触，由电源维持电势差。
4. Movement of Ions and Discharge at Electrodes | 离子运动与电极放电
dation at anode: 2 Xⁿ⁻ → X₂ + 2n e⁻. The product may be a solid, liquid, or gas, depending on the element and conditions.
放电是指离子在电极表面得到或失去电子。阳离子 Mⁿ⁺ 在阴极还原：Mⁿ⁺ + n e⁻ → M。阴离子 Xⁿ⁻ 在阳极氧化：2 Xⁿ⁻ → X₂ + 2n e⁻。产物可为固态、液态或气态，取决于元素与条件。
The ease of discharge depends on the position of the ion in the electrochemical series. More reactive metals discharge less readily, and in aqueous solutions, water can compete in redox reactions, producing H₂ or O₂.
放电的难易取决于离子在电化学序中的位置。越活泼的金属越不易放电，而在水溶液中，水可能参与氧化还原反应竞争，产生 H₂ 或 O₂。
5. Electrolysis of Molten Ionic Compounds | 熔融离子化合物的电解
tion: 2 NaCl(l) → 2 Na(l) + Cl₂(g). This is a simple decomposition with no side reactions.
在熔融 NaCl 中，仅存在 Na⁺ 和 Cl⁻。石墨阳极：2 Cl⁻ → Cl₂(g) + 2 e⁻；阴极：Na⁺ + e⁻ → Na(l)。总反应：2 NaCl(l) → 2 Na(l) + Cl₂(g)。该分解简单，无副反应。
de: 2 O²⁻ → O₂(g) + 4 e⁻, but the oxygen reacts with the carbon anode, forming CO₂ and gradually consuming it.
提取铝时，电解溶解在冰晶石（Na₃AlF₆）中的熔融 Al₂O₃。阴极：Al³⁺ + 3 e⁻ → Al(l)；碳阳极：2 O²⁻ → O₂(g) + 4 e⁻，但氧气会与碳阳极反应生成 CO₂，逐步消耗阳极。
6. Predicting Products in Aqueous Electrolysis: The Discharge Series | 水溶液电解产物预测：放电序列
In aqueous solutions, the presence of water introduces H⁺ and OH⁻ ions that can compete at the electrodes. The cation discharge order at the cathode (ease of reduction) follows: Ag⁺ > Cu²⁺ > H⁺ > Pb²⁺ > Fe²⁺ > Zn²⁺ > Al³⁺ > Mg²⁺ > Na⁺ > Ca²⁺ > K⁺.
在水溶液中，水的存在引入了 H⁺ 和 OH⁻，它们可能在电极上竞争放电。阳离子在阴极的放电顺序（还原难易）为：Ag⁺ > Cu²⁺ > H⁺ > Pb²⁺ > Fe²⁺ > Zn²⁺ > Al³⁺ > Mg²⁺ > Na⁺ > Ca²⁺ > K⁺。
For anions at the anode, the order is: I⁻ > Br⁻ > Cl⁻ > OH⁻ > NO₃⁻ > SO₄²⁻ (and other oxyanions). If a halide ion is present, it will be oxidised in preference to OH⁻, otherwise oxygen gas is released from the oxidation of water or OH⁻.
阴离子在阳极的放电顺序为：I⁻ > Br⁻ > Cl⁻ > OH⁻ > NO₃⁻ > SO₄²⁻（及其他含氧酸根）。若存在卤离子，则优先于 OH⁻ 被氧化，否则由 OH⁻ 氧化产生氧气。
7. Competing Reactions: Water vs. Ions | 竞争反应：水与离子的放电
At the anode, Cl⁻ is present and will oxidise: 2 Cl⁻ → Cl₂(g) + 2 e⁻. The solution becomes alkaline.
在稀 NaCl 溶液中，阴极反应为水的还原：2 H₂O(l) + 2 e⁻ → H₂(g) + 2 OH⁻，因为 Na⁺ 过于活泼难以放电。阳极 Cl⁻ 氧化：2 Cl⁻ → Cl₂(g
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