📚 Types of Chemical Reactions | 化学反应的类型
Welcome to this KS3 Chemistry revision guide on types of chemical reactions. In this article, you will learn how to recognise five main reaction types, write word equations, and use observable signs to decide when a chemical change has taken place.
欢迎阅读本篇 KS3 化学复习指南——化学反应的类型。本文将帮助你识别五种主要反应类型、书写文字方程式，并根据可观察的现象判断是否发生了化学变化。
1. What Is a Chemical Reaction? | 什么是化学反应？
A chemical reaction is a process in which one or more substances change into new substances with different properties. During the reaction, atoms are rearranged, but no atoms are created or destroyed.
化学反应是指一种或多种物质转变成具有不同性质的新物质的过程。在反应过程中，原子被重新排列，但原子不会被创造或消灭。
For example, when iron reacts with sulfur, the grey iron and yellow sulfur disappear, and a new black solid called iron sulfide is formed. This new substance has properties different from both iron and sulfur.
例如，当铁与硫反应时，灰色的铁和黄色的硫消失，生成一种叫做硫化铁的黑色新固体。这种新物质的性质与铁和硫都不同。
2. Signs of a Chemical Change | 化学变化的迹象
We can often tell that a chemical reaction has happened by observing one or more signs. The main signs include a colour change, bubbles of gas being produced, a precipitate forming, a temperature change, or light and sound being released.
我们通常可以通过观察一个或多个迹象来判断是否发生了化学反应。主要迹象包括颜色变化、产生气泡、生成沉淀、温度变化，或者释放出光和声音。
However, these signs are not proof on their own. Boiling water produces bubbles, but this is only a physical change because no new substance is made. You must decide whether new substances have formed.
然而，这些迹象本身并不能作为绝对证据。水沸腾会产生气泡，但这只是物理变化，因为没有新物质生成。你需要判断是否形成了新物质。
3. Reactants, Products and Word Equations | 反应物、生成物与文字方程式
In a chemical reaction, the starting substances are called reactants. The new substances made by the reaction are called products. A word equation shows the names of the reactants and products in a clear order.
在化学反应中，起始物质称为反应物，反应生成的新物质称为生成物。文字方程式按清楚的顺序表示反应物和生成物的名称。
reactant 1 + reactant 2 → product 1 + product 2
反应物 1 + 反应物 2 → 生成物 1 + 生成物 2
The arrow in the middle means 'reacts to form' or 'produces'. You should never write an equals sign in a word equation because the substances on each side are not the same.
中间的箭头表示“反应生成”或“产生”。在文字方程式中不应使用等号，因为两侧的物质并不相同。
4. Combination (Synthesis) Reactions | 化合（合成）反应
A combination reaction occurs when two or more reactants join together to form one single product. The general pattern is:
化合反应是指两种或多种反应物结合生成一种单一产物的反应。其一般模式为：
A + B → AB
A + B → AB
A common example is the reaction between hydrogen and oxygen to make water. This reaction releases a large amount of energy.
一个常见的例子是氢气与氧气反应生成水。该反应会释放大量能量。
hydrogen + oxygen → water
氢气 + 氧气 → 水
Another example is the reaction between iron and sulfur when heated. The iron and sulfur combine to form a new compound called iron sulfide.
另一个例子是加热时铁与硫的反应。铁和硫结合生成一种叫做硫化铁的新化合物。
iron + sulfur → iron sulfide
铁 + 硫 → 硫化铁
5. Decomposition Reactions | 分解反应
A decomposition reaction is the opposite of a combination reaction. One compound breaks down into two or more simpler substances. The general pattern is:
分解反应与化合反应相反。一种化合物分解成两种或多种更简单的物质。其一般模式为：
AB → A + B
AB → A + B
Many decomposition reactions need heat energy to take place. When this happens, we call it thermal decomposition. For example, copper carbonate breaks down when heated strongly.
许多分解反应需要加热才能发生。这种反应称为热分解。例如，碳酸铜在强热下会分解。
copper carbonate → copper oxide + carbon dioxide
碳酸铜 → 氧化铜 + 二氧化碳
In this reaction, the green solid copper carbonate changes into black copper oxide powder, and carbon dioxide gas is released. You can test for carbon dioxide with limewater, which turns cloudy.
在该反应中，绿色的碳酸铜固体变成黑色的氧化铜粉末，同时释放出二氧化碳气体。可以用石灰水检验二氧化碳，因为石灰水会变浑浊。
6. Combustion Reactions | 燃烧反应
Combustion is a rapid reaction between a fuel and oxygen. It is exothermic, which means it releases heat energy, and it usually produces a flame.
燃烧是燃料与氧气之间发生的快速反应。它是放热反应，会释放热能，并且通常产生火焰。
The complete combustion of a hydrocarbon fuel produces carbon dioxide and water. For example, methane burns in air according to this word equation:
碳氢化合物燃料的完全燃烧生成二氧化碳和水。例如，甲烷在空气中燃烧的文字方程式如下：
methane + oxygen → carbon dioxide + water
甲烷 + 氧气 → 二氧化碳 + 水
Combustion is very important in everyday life because it is used in car engines, gas stoves, and power stations. However, incomplete combustion can produce carbon monoxide, which is a poisonous gas.
燃烧在日常生活中非常重要，因为汽车发动机、燃气灶和发电站都使用燃烧反应。但不完全燃烧会产生一氧化碳，这是一种有毒气体。
7. Displacement Reactions | 置换反应
A displacement reaction happens when a more reactive element takes the place of a less reactive element in a compound. The general pattern is:
置换反应是指较活泼的元素取代化合物中较不活泼的元素。其一般模式为：
A + BC → AC + B
A + BC → AC + B
A classic example is placing zinc metal into copper sulfate solution. Zinc is more reactive than copper, so it displaces copper from the solution.
一个经典例子是将锌金属放入硫酸铜溶液中。锌比铜活泼，因此它从溶液中置换出铜。
zinc + copper sulfate → zinc sulfate + copper
锌 + 硫酸铜 → 硫酸锌 + 铜
You can observe the blue copper sulfate solution becoming paler, while reddish-brown copper metal coats the zinc. This colour change is strong evidence that a displacement reaction has occurred.
可以观察到蓝色的硫酸铜溶液逐渐变浅，同时红棕色的铜金属覆盖在锌表面。这种颜色变化是发生置换反应的有力证据。
8. Neutralisation Reactions | 中和反应
Neutralisation occurs when an acid reacts with a base or an alkali to form a salt and water. The general word equation is:
中和反应是指酸与碱或可溶性碱反应生成盐和水。其一般文字方程式为：
acid + base → salt + water
酸 + 碱 → 盐 + 水
For example, hydrochloric acid reacts with sodium hydroxide solution to produce sodium chloride (common salt) and water.
例如，盐酸与氢氧化钠溶液反应生成氯化钠（食盐）和水。
hydrochloric acid + sodium hydroxide → sodium chloride + water
盐酸 + 氢氧化钠 → 氯化钠 + 水
Neutralisation is useful in many contexts, such as reducing stomach acid with indigestion tablets, treating acidic soil, and neutralising acidic waste before it is released into rivers.
中和反应在许多情境中很有用，例如用抗酸药片缓解胃酸过多、改良酸性土壤，以及在酸性废水排入河流前进行中和处理。
9. Precipitation Reactions | 沉淀反应
A precipitation reaction happens when two solutions react to form an insoluble solid called a precipitate. The solid appears as tiny particles that make the mixture cloudy.
沉淀反应是指两种溶液反应生成不溶性固体（称为沉淀）的反应。这种固体会以微小颗粒的形式出现，使混合物变浑浊。
A well-known example is the reaction between lead nitrate solution and potassium iodide solution. A bright yellow precipitate of lead iodide is produced.
一个著名的例子是硝酸铅溶液与碘化钾溶液的反应，会生成亮黄色的碘化铅沉淀。
lead nitrate + potassium iodide → lead iodide + potassium nitrate
硝酸铅 + 碘化钾 → 碘化铅 + 硝酸钾
The precipitate is a new substance, so this is definitely a chemical change. Precipitation reactions are also used in water treatment to remove unwanted dissolved substances.
沉淀物是一种新物质，因此这一定是化学变化。沉淀反应也用于水处理，以去除不需要的溶解性物质。
10. Exothermic and Endothermic Reactions | 放热与吸热反应
Chemical reactions involve energy changes as well as changes in substances. An exothermic reaction releases energy to the surroundings, usually as heat, so the temperature rises.
化学反应不仅涉及物质变化，还涉及能量变化。放热反应向周围环境释放能量，通常以热的形式释放，因此温度升高。
Combustion and neutralisation are two important examples of exothermic reactions. In contrast, an endothermic reaction absorbs energy from the surroundings, so the temperature falls.
燃烧和中和是放热反应的两个重要例子。相反，吸热反应从周围环境吸收能量，因此温度下降。
Thermal decomposition is usually endothermic because it needs a continuous supply of heat to break compounds apart. For example, copper carbonate only decomposes while it is being heated strongly.
热分解通常是吸热反应，因为它需要持续供热来分解化合物。例如，碳酸铜只有在被强热时才会分解。
11. How to Identify a Reaction Type from an Equation | 如何从方程式判断反应类型
You can often classify a reaction by looking at the pattern of reactants and products in its word equation. Use this simple summary table to help you.
通常可以通过观察文字方程式中反应物和生成物的模式来判断反应类型。可以使用下面的简单总结表来帮助你。
| Reaction type | 反应类型 | Pattern | 模式 | Example | 例子 |
|---|---|---|
| Combination | 化合 | A + B → AB | hydrogen + oxygen → water |
| Decomposition | 分解 | AB → A + B | copper carbonate → copper oxide + carbon dioxide |
| Combustion | 燃烧 | fuel + oxygen → oxides | methane + oxygen → carbon dioxide + water |
| Displacement | 置换 | A + BC → AC + B | zinc + copper sulfate → zinc sulfate + copper |
| Neutralisation | 中和 | acid + base → salt + water | hydrochloric acid + sodium hydroxide → sodium chloride + water |
| Precipitation | 沉淀 | two solutions → solid + solution | lead nitrate + potassium iodide → lead iodide + potassium nitrate |
When you see oxygen as a reactant and carbon dioxide and water as products, think of combustion. When an acid and a base appear as reactants, think of neutralisation.
当你看到氧气作为反应物、二氧化碳和水作为生成物时，要考虑燃烧反应。当反应物中出现酸和碱时，要考虑中和反应。
12. Common Misconceptions and Exam Tips | 常见误区与考试提示
One common mistake is to confuse dissolving with a chemical reaction. When salt dissolves in water, the salt can be recovered by evaporation, so no new substance is formed. Dissolving is a physical change, not a chemical reaction.
一个常见的错误是把溶解与化学反应混为一谈。盐溶于水时，可以通过蒸发重新得到盐，因此没有新物质生成。溶解是物理变化，不是化学反应。
Another misconception is that a colour change always means a chemical reaction. Some physical changes, such as mixing food colouring into water, also show a colour change. Always ask whether new substances with new properties have been made.
另一个误区是认为颜色变化一定意味着发生了化学反应。有些物理变化，例如把食用色素混入水中，也会出现颜色变化。要始终思考是否生成了具有新性质的新物质。
In exams, always write word equations in the correct order: reactants on the left, products on the right, and an arrow in the middle. Include all the names exactly as given in the question, and never use an equals sign.
在考试中，书写文字方程式时要遵循正确顺序：反应物在左边，生成物在右边，中间用箭头连接。准确使用题目中给出的名称，不要使用等号。
Finally, remember that combustion always needs oxygen. If a fuel burns in a closed container, the reaction stops when the oxygen runs out. This is why fires can be put out by covering them with a fire blanket or carbon dioxide.
最后，请记住燃烧总是需要氧气。如果燃料在密闭容器中燃烧，氧气耗尽后反应就会停止。这就是可以用防火毯或二氧化碳灭火的原因。
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