📚 Electrochemical Cells: Principles and Electrode Reactions in IB Chemistry | IB化学：电化学电池的原理与电极反应
Electrochemistry is a central topic in IB Chemistry that links redox reactions to everyday energy production and industrial electrolysis. Understanding the principles of electrochemical cells and mastering the writing of electrode reactions are essential skills for both Standard Level and Higher Level students.
电化学是IB化学的核心主题，它将氧化还原反应与日常能源生产和工业电解紧密相连。理解电化学电池的原理并掌握电极反应的书写，是标准级和高等级学生都必须具备的关键技能。
1. Redox Revisited | 回顾氧化还原
In every redox reaction, one species loses electrons while another gains them. The substance losing electrons is oxidised and acts as a reducing agent; the substance gaining electrons is reduced and acts as an oxidising agent.
在任何氧化还原反应中，一种物质失去电子，另一种物质则获得电子。失去电子的物质被氧化，充当还原剂；获得电子的物质被还原，充当氧化剂。
Consider the zinc–copper system: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). Zinc is oxidised because its oxidation number increases from 0 to +2, while copper(II) is reduced from +2 to 0.
以锌-铜体系为例：Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)。锌被氧化，因为其氧化数从0升高到+2；而铜(II)被还原，氧化数从+2降为0。
2. Half-Cells and Half-Reactions | 半电池与半反应
An electrochemical cell separates the oxidation and reduction processes into two half-cells. Each half-cell contains a conjugate redox couple, often written as Ox/Red, for example Zn²⁺/Zn or Cu²⁺/Cu.
电化学电池将氧化过程和还原过程分隔在两个半电池中。每个半电池包含一个共轭氧化还原电对，通常写作 Ox/Red，例如 Zn²⁺/Zn 或 Cu²⁺/Cu。
The two half-reactions for the zinc–copper cell are:
锌-铜电池的两个半反应为：
Zn(s) → Zn²⁺(aq) + 2e⁻ (oxidation)
Cu²⁺(aq) + 2e⁻ → Cu(s) (reduction)
Each half-reaction is written in the direction shown in the electrochemical series, and the overall cell reaction is obtained by combining them so that electrons cancel.
每个半反应按电化学序列所示方向书写，将两个半反应组合并消去电子后，即可得到总电池反应。
3. Anode and Cathode | 阳极与阴极
The anode is the electrode where oxidation occurs. The cathode is the electrode where reduction occurs. Because electrons always flow from anode to cathode in the external circuit, the anode is the negative electrode in a voltaic (galvanic) cell but the positive electrode in an electrolytic cell.
阳极是发生氧化的电极，阴极是发生还原的电极。由于电子在外电路中总是从阳极流向阴极，因此在原电池中阳极为负极，而在电解池中阳极却为正极。
A useful memory aid is “An Ox” and “Red Cat”: anode = oxidation, cathode = reduction.
一个有用的记忆口诀是 “An Ox” 和 “Red Cat”：阳极 = 氧化，阴极 = 还原。
4. Standard Cell Notation | 标准电池符号
The international convention for representing a cell is a shorthand written in a specific order. A single vertical line | represents a phase boundary, and a double vertical line || represents a salt bridge or porous barrier.
国际通用的电池表示法是一种按特定顺序书写的简写符号。单竖线 | 代表相界，双竖线 || 代表盐桥或多孔隔膜。
For the zinc–copper cell, the standard cell notation is:
对于锌-铜电池，标准电池符号为：
Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)
The anode half-cell is always written on the left, and the cathode half-cell is written on the right.
阳极半电池始终写在左侧，阴极半电池写在右侧。
5. The Standard Hydrogen Electrode | 标准氢电极
Because the absolute potential of a single electrode cannot be measured, electrode potentials are measured relative to a reference electrode. The internationally accepted reference is the standard hydrogen electrode (SHE), assigned a potential of exactly 0.00 V.
由于单个电极的绝对电位无法测量，电极电位必须以参比电极为标准进行测量。国际公认的参比电极是标准氢电极（SHE），其电位被指定为恰好0.00 V。
The SHE consists of hydrogen gas at 1 atm bubbling over a platinum electrode immersed in a 1 mol dm⁻³ H⁺ solution at 298 K:
SHE由1 atm的氢气鼓泡通过铂电极构成，铂电极浸入298 K、浓度为1 mol dm⁻³的H⁺溶液中：
2H⁺(aq) + 2e⁻ ⇌ H₂(g) E° = 0.00 V
The platinum is inert and only provides a surface for electron transfer.
铂是惰性的，仅提供电子转移的表面。
6. Standard Electrode Potentials | 标准电极电位
The standard electrode potential E° is the voltage measured when a half-cell is connected to the SHE under standard conditions: 298 K, 1 mol dm⁻³ for solutions, and 1 atm for gases.
标准电极电位 E° 是半电池在标准条件下与SHE连接时测得的电压。标准条件为：298 K、溶液浓度1 mol dm⁻³、气体压强1 atm。
A positive E° indicates that the half-cell is more likely to undergo reduction relative to the SHE, while a negative E° indicates it is a stronger reducing agent than H₂.
E°为正值表示该半电池相对于SHE更容易发生还原；E°为负值则表示它是比H₂更强的还原剂。
| Half-reaction | E° / V |
| Zn²⁺(aq) + 2e⁻ ⇌ Zn(s) | -0.76 |
| Cu²⁺(aq) + 2e⁻ ⇌ Cu(s) | +0.34 |
| 2H⁺(aq) + 2e⁻ ⇌ H₂(g) | 0.00 |
7. Calculating Cell Potential | 计算电池电位
The standard cell potential E°cell is calculated using the equation E°cell = E°cathode – E°anode. The larger (more positive) electrode potential is the cathode, and the smaller (more negative) one is the anode.
标准电池电位 E°cell 使用公式 E°cell = E°cathode – E°anode 计算。电极电位较大（更正）的为阴极，较小（更负）的为阳极。
For the zinc–copper cell:
对于锌-铜电池：
E°cell = (+0.34 V) – (-0.76 V) = +1.10 V
A positive E°cell indicates a spontaneous reaction under standard conditions. The number of electrons transferred does not affect E°cell, since electrode potentials are intensive properties.
E°cell为正值表明该反应在标准条件下是自发的。转移电子的数目不影响 E°cell，因为电极电位是强度性质。
8. The Voltaic Cell | 原电池
A voltaic cell converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two half-cells connected by a salt bridge and an 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。它由两个半电池组成，通过盐桥和外电路导线连接。
The salt bridge contains an inert electrolyte such as KNO₃ and has two essential functions: it completes the electrical circuit and maintains charge balance. Without a salt bridge, the cell would stop producing current almost immediately.
盐桥含有诸如KNO₃之类的惰性电解质，具有两个基本功能：接通电路并维持电荷平衡。如果没有盐桥，电池几乎会立即停止产生电流。
In the zinc–copper voltaic cell, zinc is oxidised at the anode, producing Zn²⁺ ions and leaving electrons on the electrode. Electrons flow through the external circuit to the copper electrode, where Cu²⁺ ions are reduced to copper metal.
在锌-铜原电池中，锌在阳极被氧化，生成Zn²⁺离子并留下电子。电子通过外电路流向铜电极，Cu²⁺离子在此被还原为铜金属。
9. Electrolytic Cells | 电解池
An electrolytic cell uses electrical energy to drive a non-spontaneous redox reaction. The anode and cathode are connected to a direct current power supply. The anode is positive, and the cathode is negative.
电解池利用电能驱动非自发的氧化还原反应。阳极和阴极连接到直流电源。阳极为正极，阴极为负极。
During electrolysis, oxidation occurs at the anode and reduction occurs at the cathode. Positive ions migrate to the cathode, and negative ions migrate to the anode.
电解过程中，阳极发生氧化，阴极发生还原。阳离子向阴极迁移，阴离子向阳极迁移。
For molten sodium chloride, the reactions are:
以熔融氯化钠为例，电极反应为：
Cathode: Na⁺(l) + e⁻ → Na(l)
Anode: 2Cl⁻(l) → Cl₂(g) + 2e⁻
10. Faraday’s Laws | 法拉第定律
Faraday’s first law states that the mass of substance produced at an electrode is proportional to the quantity of electric charge passed. The charge Q is calculated from current I and time t: Q = I × t.
法拉第第一定律指出，电极上产生的物质质量与通过的电荷量成正比。电荷量Q由电流I和时间t计算：Q = I × t。
m = (Q × M) / (n × F)
Here, m is mass, M is molar mass, n is the number of electrons transferred per ion, F is the Faraday constant (96 500 C mol⁻¹), and Q is the charge in coulombs.
其中m是质量，M是摩尔质量，n是每个离子转移的电子数，F是法拉第常数（96 500 C mol⁻¹），Q是以库仑为单位的电荷量。
For example, to deposit 1 mol of copper from Cu²⁺ requires 2 mol of electrons, so 2 × 96 500 = 193 000 C of charge.
例如，从Cu²⁺沉积1 mol铜需要2 mol电子，因此需要 2 × 96 500 = 193 000 C 的电荷。
11. Common Exam Pitfalls | 常见考试陷阱
Students often mix up the sign of the anode in voltaic versus electrolytic cells. In a voltaic cell the anode is negative; in an electrolytic cell the anode is positive. Always identify whether the process is spontaneous first.
学生经常混淆原电池和电解池中阳极的符号。原电池中阳极为负极；电解池中阳极则为正极。务必首先判断过程是否自发。
Another common error is multiplying E° values when balancing half-reactions. Do not multiply electrode potentials; only the quantities of electrons may need to be balanced.
另一个常见错误是在配平半反应时对 E° 值进行乘法运算。切勿乘以电极电位；只可能需要配平电子的数量。
Also remember that gases in half-cells are written on the same side as the electrode, as in Pt | H₂(g) | H⁺(aq).
还要记住，气体在半电池中写在电极一侧，例如 Pt | H₂(g) | H⁺(aq)。
12. Practical Applications | 实际应用
Voltaic cells are used in everyday batteries such as alkaline batteries and lithium-ion batteries. Lithium-ion cells have a high E°cell and low molar mass, making them ideal for portable electronics.
原电池用于日常电池，如碱性电池和锂离子电池。锂离子电池具有高 E°cell 和低摩尔质量，非常适合便携式电子设备。
Electrolytic cells are used in electroplating, aluminium extraction, and the chlor-alkali industry. In electroplating, the object to be coated is made the cathode so that metal ions in solution are reduced onto its surface.
电解池用于电镀、铝的冶炼和氯碱工业。在电镀中，待镀物体作为阴极，使溶液中的金属离子在其表面被还原。
From a mobile phone battery to the refining of copper, electrochemical principles are everywhere. Mastering half-reactions, cell notation, and E° calculations is your key to success in IB Chemistry.
从手机电池到铜的电解精炼，电化学原理无处不在。掌握半反应、电池符号和 E° 计算是你在IB化学中取得好成绩的关键。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导