📚 Electrode Potentials | 电极电势
Electrode potentials are the driving force behind every electrochemical cell, from simple laboratory half-cells to the lithium-ion batteries powering modern devices. They allow chemists to compare the tendency of different species to gain or lose electrons and to predict whether a redox reaction is feasible under standard conditions.
电极电势是每个电化学电池背后的驱动力，从简单的实验室半电池到为现代设备供电的锂离子电池。它们让化学家能够比较不同物质得到或失去电子的倾向，并预测氧化还原反应在标准条件下是否可行。
1. Redox Basics and Half Equations | 氧化还原基础与半反应方程式
Redox chemistry is the study of electron transfer. Oxidation is the loss of electrons, and reduction is the gain of electrons. These two processes always occur together because electrons cannot accumulate in solution.
氧化还原化学研究的是电子转移。氧化是失去电子，还原则是得到电子。这两个过程总是同时发生，因为电子不可能在溶液中积累。
A half-equation shows the electron transfer for one species only. For example, zinc metal can lose two electrons to form zinc ions, while copper(II) ions can gain two electrons to form copper metal.
半反应方程式只表示一种物质的电子转移。例如，锌金属可以失去两个电子形成锌离子，而铜(II)离子可以得到两个电子形成铜金属。
Zn(s) → Zn²⁺(aq) + 2e⁻
Cu²⁺(aq) + 2e⁻ → Cu(s)
2. What Is an Electrode Potential? | 什么是电极电势？
When a metal rod is placed in a solution of its own ions, an equilibrium is set up at the surface between metal atoms and metal ions. The position of this equilibrium creates an electrical potential difference between the metal and the solution. This is called the electrode potential.
当金属棒放入其自身离子的溶液中时，金属表面会在金属原子和金属离子之间建立一个平衡。这个平衡的位置会在金属和溶液之间产生电势差，这就是电极电势。
Mⁿ⁺(aq) + n e⁻ ⇌ M(s)
A single electrode potential cannot be measured directly because any voltmeter needs two contacts. Therefore all electrode potentials are measured relative to a chosen reference electrode.
单个电极电势无法直接测量，因为任何电压表都需要两个接触点。因此，所有电极电势都是相对于选定的参比电极来测量的。
The standard electrode potential, E°, of a half-cell is the electromotive force of that half-cell connected to the standard hydrogen electrode, measured under standard conditions of 298 K, 100 kPa and 1.00 mol dm⁻³ ion concentration.
半电池的标准电极电势 E° 是指该半电池与标准氢电极相连时产生的电动势，在 298 K、100 kPa 和 1.00 mol dm⁻³ 离子浓度的标准条件下测得。
3. The Standard Hydrogen Electrode | 标准氢电极
The standard hydrogen electrode, SHE, is the reference electrode used to define standard electrode potentials. By convention, its potential is assigned a value of exactly 0.00 V at all temperatures.
标准氢电极是用于定义标准电极电势的参比电极。按照规定，它在所有温度下的电势都被定义为零，即 0.00 V。
The SHE consists of platinized platinum foil immersed in 1.00 mol dm⁻³ H⁺(aq). Hydrogen gas at a pressure of 100 kPa bubbles over the surface at 298 K. Platinum provides an inert conducting surface and adsorbs hydrogen gas.
标准氢电极由镀铂的铂片浸入 1.00 mol dm⁻³ H⁺(aq) 溶液中构成。在 298 K 下，压强为 100 kPa 的氢气在电极表面不断通入。铂提供惰性导电表面并吸附氢气。
2H⁺(aq) + 2e⁻ ⇌ H₂(g) E° = 0.00 V
Standard conditions must be stated clearly: temperature 298 K, pressure 100 kPa, and all ion concentrations 1.00 mol dm⁻³. Any change in these conditions will change the measured potential.
标准条件必须明确指出：温度 298 K，压强 100 kPa，所有离子浓度均为 1.00 mol dm⁻³。这些条件中任何一项发生变化都会改变测得的电势。
4. Measuring Standard Electrode Potentials | 标准电极电势的测量
To measure the standard electrode potential of a half-cell, it is connected to the standard hydrogen electrode using a salt bridge and a high-resistance voltmeter. The salt bridge completes the circuit by allowing ions to flow without letting solutions mix.
要测量半电池的标准电极电势，需要将其通过盐桥和高电阻电压表与标准氢电极相连。盐桥允许离子流动以构成回路，同时避免两种溶液混合。
For example, a zinc half-cell is set up with zinc metal in 1.00 mol dm⁻³ Zn²⁺(aq). The cell diagram is written with the SHE on the right by convention when reporting standard electrode potentials.
例如，将锌金属浸入 1.00 mol dm⁻³ Zn²⁺(aq) 溶液中构成锌半电池。报告标准电极电势时，按照惯例将标准氢电极写在右侧来表示电池图式。
Zn(s) | Zn²⁺(aq) || H⁺(aq) | H₂(g) | Pt(s)
The voltmeter reading is −0.76 V. Since the standard hydrogen electrode has a potential of 0.00 V, this means E°(Zn²⁺/Zn) = −0.76 V. The negative sign shows that zinc is more willing to lose electrons than hydrogen.
电压表读数为 −0.76 V。由于标准氢电极的电势为 0.00 V，因此 E°(Zn²⁺/Zn) = −0.76 V。负号说明锌比氢更倾向于失去电子。
5. The Electrochemical Series | 电化学序
When standard electrode potentials are arranged in order from most negative to most positive, they form the electrochemical series. The more negative the value, the stronger the reducing agent on the right-hand side of the half-equation. The more positive the value, the stronger the oxidising agent on the left-hand side.
将标准电极电势从最负到最正依次排列，就得到电化学序。数值越负，半反应方程式右侧的还原态物质还原性越强；数值越正，左侧的氧化态物质氧化性越强。
This series lets chemists compare the relative strengths of oxidising and reducing agents. For example, zinc with E° = −0.76 V is a much stronger reducing agent than copper with E° = +0.34 V.
电化学序使化学家能够比较氧化剂和还原剂的相对强弱。例如，E° = −0.76 V 的锌比 E° = +0.34 V 的铜具有更强的还原性。
| Half-reaction | E° / V |
|---|---|
| Li⁺ + e⁻ ⇌ Li | −3.04 |
| Zn²⁺ + 2e⁻ ⇌ Zn | −0.76 |
| Fe²⁺ + 2e⁻ ⇌ Fe | −0.44 |
| 2H⁺ + 2e⁻ ⇌ H₂ | 0.00 |
| Cu²⁺ + 2e⁻ ⇌ Cu | +0.34 |
| Fe³⁺ + e⁻ ⇌ Fe²⁺ | +0.77 |
| Ag⁺ + e⁻ ⇌ Ag | +0.80 |
| Cl₂ + 2e⁻ ⇌ 2Cl⁻ | +1.36 |
| MnO₄⁻ + 8H⁺ + 5e⁻ ⇌ Mn²⁺ + 4H₂O | +1.51 |
6. Calculating Cell Potentials | 计算电池电动势
For a cell diagram written with oxidation on the left and reduction on the right, the standard cell potential is calculated from the difference between the two standard electrode potentials.
对于左侧为氧化反应、右侧为还原反应的电池图式，标准电池电动势可由两个标准电极电势之差计算。
E°cell = E°(right-hand electrode) − E°(left
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