Cells and Batteries | 电化学电池与电池组

📚 Cells and Batteries | 电化学电池与电池组

Electrochemical cells convert chemical energy into electrical energy via redox reactions. A cell consists of two half-cells connected by a salt bridge, and a battery is simply one or more cells used as a practical source of electricity. In Cambridge A-Level Chemistry, you need to link half-equations, standard electrode potentials, cell diagrams, and real battery systems such as fuel cells and lithium-ion cells.

电化学电池通过氧化还原反应将化学能转化为电能。一个电池由两个半电池通过盐桥连接而成，电池组则是将一个或多个电池用作实际电源。在剑桥 A-Level 化学中，你需要把半反应方程式、标准电极电势、电池图示以及燃料电池和锂离子电池等真实电池系统联系起来。

1. Redox Foundations and Half-Equations | 氧化还原基础与半反应方程式

Redox reactions are the chemical basis of all cells. Oxidation is loss of electrons, and reduction is gain of electrons. In a cell, oxidation occurs at the anode and reduction occurs at the cathode. Every electrode reaction can be written as a half-equation showing electron transfer.

氧化还原反应是所有电池的化学基础。氧化是失去电子，还原是得到电子。在电池中，阳极发生氧化反应，阴极发生还原反应。每个电极反应都可以写成表示电子转移的半反应方程式。

For a zinc-copper cell, the zinc half-equation is Zn(s) ⇌ Zn²⁺(aq) + 2e⁻, and the copper half-equation is Cu²⁺(aq) + 2e⁻ ⇌ Cu(s). These half-equations are reversible, so the direction depends on the other half-cell connected.

对于锌铜电池，锌的半反应方程式为 Zn(s) ⇌ Zn²⁺(aq) + 2e⁻，铜的半反应方程式为 Cu²⁺(aq) + 2e⁻ ⇌ Cu(s)。这些半反应是可逆的，因此其方向取决于所连接的另一半电池。

2. Electrochemical Cells: Construction and Cell Diagrams | 电化学电池的构造与电池图示

A simple electrochemical cell is made from two metal/metal-ion half-cells connected by a wire and a salt bridge. The salt bridge contains an ionic solution such as KNO₃ and completes the circuit by allowing ions to move without mixing the half-cell solutions.

简单的电化学电池由两个金属/金属离子半电池通过导线和盐桥连接而成。盐桥中含有如 KNO₃ 的离子溶液，它允许离子移动以构成回路，但不使两个半电池溶液混合。

The standard cell diagram is written with the anode on the left and the cathode on the right. A single vertical line shows a phase boundary, and a double vertical line shows the salt bridge. For example:

标准电池图示将阳极写在左侧，阴极写在右侧。单竖线表示相界面，双竖线表示盐桥。例如：

Zn(s)|Zn²⁺(aq)||Cu²⁺(aq)|Cu(s)

In this cell, zinc is oxidised and copper(II) ions are reduced. Electrons flow from the zinc electrode to the copper electrode in the external circuit.

在这个电池中，锌被氧化，铜(II) 离子被还原。电子在外部电路中从锌电极流向铜电极。

3. Standard Electrode Potentials and the Hydrogen Electrode | 标准电极电势与氢电极

The standard electrode potential E° of a half-cell is measured under standard conditions: 298 K, 100 kPa pressure, and 1.0 mol dm⁻³ ion concentration. It is measured relative to the standard hydrogen electrode, which is assigned a potential of 0.00 V.

半电池的标准电极电势 E° 是在标准条件下测量的：298 K、100 kPa 压力以及 1.0 mol dm⁻³ 离子浓度。它是相对于标准氢电极测量的，标准氢电极的电势被规定为 0.00 V。

The hydrogen half-cell consists of hydrogen gas at 100 kPa bubbling over a platinum electrode in contact with 1.0 mol dm⁻³ H⁺ ions. Platinum is used because it is inert and provides a surface for the reaction:

氢半电池由 100 kPa 的氢气在铂电极表面吹泡，并与 1.0 mol dm⁻³ H⁺ 离子接触组成。使用铂是因为它具有惰性，并为反应提供表面：

2H⁺(aq) + 2e⁻ ⇌ H₂(g) E° = 0.00 V

A more negative E° means a stronger reducing agent and a greater tendency to lose electrons. A more positive E° means a stronger oxidising agent and a greater tendency to gain electrons.

E° 越负，说明还原性越强，失去电子的倾向越大。E° 越正，说明氧化性越强，得到电子的倾向越大。

4. Calculating Cell EMF and Predicting Feasibility | 计算电池电动势与判断反应可行性

The standard cell potential E°cell is calculated by subtracting the standard potential of the anode half-cell from that of the cathode half-cell. Use the formula E°cell = E°cathode − E°anode, where both values are the reduction potentials from the electrochemical series.

标准电池电动势 E°cell 通过从阴极半电池的标准电势中减去阳极半电池的标准电势来计算。使用公式 E°cell = E°cathode − E°anode，其中两个值都是电化学序中的还原电势。

E°cell = E°cathode − E°anode

For a reaction to be feasible under standard conditions, E°cell must be positive. For example, combining Zn²⁺/Zn (E° = −0.76 V) and Cu²⁺/Cu (E° = +0.34 V) gives E°cell = +0.34 − (−0.76) = +1.10 V, so the reaction is feasible.

要使反应在标准条件下可行，E°cell 必须为正。例如，将 Zn²⁺/Zn (E° = −0.76 V) 与 Cu²⁺/Cu (E° = +0.34 V) 组合，得到 E°cell = +0.34 − (−0.76) = +1.10 V，所以反应可行。

Remember: do not multiply the E° value by the number of electrons when balancing equations, because electrode potential is an intensive property.

请记住：配平方程式时不要将 E° 值乘以电子数，因为电极电势是一种强度性质。

5. Limitations of Standard Electrode Potentials | 标准电极电势的局限性

Standard electrode potentials only predict feasibility under standard conditions. If concentration, temperature, or pressure changes, the cell potential changes and the reaction may become non-spontaneous. The Nernst equation can be used to adjust

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