📚 Metal Displacement Reactions | 金属置换反应
At KS3, one of the most useful patterns in chemistry is that a more reactive metal can push a less reactive metal out of its compound. This type of reaction is called a displacement reaction, and it helps us predict whether reactions will happen in solutions and metal compounds.
在 KS3 阶段，化学中一个非常有用的规律是：较活泼的金属可以把较不活泼的金属从其化合物中“挤”出来。这类反应叫做置换反应，它能帮助我们预测反应是否会发生在溶液和金属化合物中。
1. What Is a Displacement Reaction? | 什么是置换反应？
A displacement reaction happens when a more reactive element takes the place of a less reactive element in a compound. In metal displacement, one metal replaces another metal from its salt solution or oxide.
当较活泼的元素取代化合物中较不活泼的元素时，就会发生置换反应。在金属置换反应中，一种金属会从另一种金属的盐溶液或氧化物中将其替换出来。
The metal that is added must be more reactive than the metal already in the compound. If it is less reactive, no reaction occurs.
加入的金属必须比化合物中已有的金属更活泼。如果它的活泼性较弱，则不会发生反应。
2. The Reactivity Series | 金属活动性顺序
The reactivity series is a list of metals arranged from the most reactive to the least reactive. It helps us decide whether one metal can displace another. A typical KS3 order from most to least reactive is: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver and gold.
金属活动性顺序是把金属从最活泼到最不活泼排列出来的一张表。它帮助我们判断一种金属能否置换另一种金属。KS3 常见的顺序从最活泼到最不活泼为：钾、钠、钙、镁、铝、锌、铁、铅、铜、银和金。
A metal higher in the series can displace a metal lower in the series from a solution of its compound. A metal lower in the series cannot displace a metal higher up.
在活动性顺序中位置靠前的金属，可以从位置靠后的金属化合物溶液中把该金属置换出来。位置靠后的金属不能置换位置靠前的金属。
K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au
3. Why Displacement Happens | 置换反应为什么会发生
Metals differ in how easily they form positive ions in solution. A more reactive metal loses electrons more readily than a less reactive metal. When a reactive metal is placed in a solution containing ions of a less reactive metal, the more reactive metal atoms lose electrons and enter the solution as positive ions. The ions of the less reactive metal gain electrons and form neutral atoms.
金属在溶液中形成正离子的难易程度不同。较活泼的金属比较不活泼的金属更容易失去电子。当把活泼金属放入含有较不活泼金属离子的溶液中时，活泼金属原子会失去电子，并以正离子形式进入溶液；较不活泼金属的离子则得到电子，变成中性原子。
At KS3 you do not need to explain every electron transfer, but thinking about winning the compound helps. The more reactive metal has a stronger pull on the non-metal part of the compound, so it takes over and releases the less reactive metal.
在 KS3 阶段，你不需要解释每一个电子转移过程，但可以理解为“争夺”化合物。较活泼的金属对化合物中的非金属部分吸引力更强，因此它会取而代之，使较不活泼的金属被释放出来。
4. The General Pattern | 置换反应的一般规律
The general pattern for a metal displacement reaction is: metal A + compound of metal B → compound of metal A + metal B. Metal A must be more reactive than metal B for the reaction to happen.
金属置换反应的一般规律是：金属 A + 金属 B 的化合物 → 金属 A 的化合物 + 金属 B。金属 A 必须比金属 B 更活泼，反应才能发生。
A + BC → AC + B
As a word equation, this can be written as: iron + copper sulfate → iron sulfate + copper. In this equation, iron is more reactive than copper, so it replaces copper in the sulfate compound.
用文字方程式可以写成：铁 + 硫酸铜 → 硫酸铁 + 铜。在这个方程式中，铁比铜更活泼，因此它取代了硫酸盐化合物中的铜。
5. Iron and Copper(II) Sulfate | 铁与硫酸铜
Iron is more reactive than copper, so iron displaces copper from copper(II) sulfate solution. During the reaction, the iron nail becomes coated with a reddish-brown layer of copper and the blue colour of the solution fades.
铁比铜更活泼，因此铁能从硫酸铜溶液中置换出铜。反应过程中，铁钉表面会覆盖一层红棕色的铜，溶液的蓝色会逐渐变浅。
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
The symbols s and aq show that iron and copper are solids, while the sulfates are dissolved in water. The reaction is often used in schools because the colour change is easy to see.
符号 s 和 aq 分别表示铁和铜是固体，而硫酸盐溶解在水中。这个反应经常在学校里使用，因为颜色变化很容易观察。
6. Zinc and Copper(II) Sulfate | 锌与硫酸铜
Zinc is also more reactive than copper, so zinc can displace copper from copper sulfate solution. When zinc powder or granules are added, copper metal forms and the blue solution becomes paler.
锌也比铜更活泼，因此锌能从硫酸铜溶液中置换出铜。加入锌粉或锌粒后，会生成铜金属，蓝色溶液会变浅。
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Compared with iron, zinc reacts faster and may release more heat. This shows that zinc is higher in the reactivity series than iron as well as copper.
与铁相比，锌反应更快，而且可能释放更多热量。这表明锌在活动性顺序中的位置不仅高于铜，也高于铁。
7. Magnesium and Copper(II) Sulfate | 镁与硫酸铜
Magnesium is even more reactive than zinc. When magnesium ribbon is placed in copper sulfate solution, copper forms very quickly and the blue colour can disappear. The reaction is exothermic, so the test tube feels warm.
镁比锌更活泼。把镁条放入硫酸铜溶液中时，铜会很快生成，蓝色可能完全消失。该反应是放热反应，因此试管会感觉发热。
Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s)
Some bubbles may also be seen if magnesium reacts with water in the solution. The main evidence for displacement is still the formation of copper metal and the loss of blue colour.
如果镁与溶液中的水发生反应，还可能会看到一些气泡。但置换反应的主要证据仍然是铜金属的生成和蓝色消失。
8. Observing Displacement Reactions | 观察置换反应
To identify a displacement reaction, look for evidence such as a colour change in the solution, a new metal coating on the solid, or a temperature rise. Not all of these are always visible at the same time.
要判断是否发生了置换反应，可以观察以下证据：溶液颜色变化、固体表面出现新的金属覆盖层，或者温度升高。这些现象不一定同时出现。
For example, copper sulfate solution is blue. When iron, zinc or magnesium is added, the solution becomes paler or even colourless because Cu²⁺ ions are removed and the less-coloured ions of iron, zinc or magnesium take their place.
例如，硫酸铜溶液是蓝色的。加入铁、锌或镁后，溶液会变浅甚至变为无色，因为 Cu²⁺ 离子被除去，取而代之的是颜色较浅的铁、锌或镁离子。
| Metal added | Observation | Reason |
|---|---|---|
| Iron | Pink-brown copper coating, blue fades | Iron displaces copper |
| Zinc | Brown copper powder, blue fades | Zinc displaces copper |
| Magnesium | Fast copper formation, blue fades quickly | Magnesium is more reactive |
9. Ionic View (Simple) | 简单离子视角
In copper sulfate solution, the compound exists as Cu²⁺ ions and SO₄²⁻ ions. When iron is added, iron atoms lose electrons to form Fe²⁺ ions, while Cu²⁺ ions gain electrons to form copper atoms. The sulfate ions remain in solution unchanged.
在硫酸铜溶液中，化合物以 Cu²⁺ 离子和 SO₄²⁻ 离子形式存在。加入铁后，铁原子失去电子形成 Fe²⁺ 离子，同时 Cu²⁺ 离子得到电子形成铜原子。硫酸根离子留在溶液中，不发生变化。
Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)
The sulfate ion is a spectator ion, which means it does not take part in the main change. This simplified ionic equation focuses on the metals only.
硫酸根离子是一种旁观离子，意思是不参与主要变化。这个简化的离子方程式只关注金属的变化。
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