📚 How Does a Catalyst Work: KS3 CIE Mark Scheme Guide | KS3 CIE 催化剂工作原理评分标准指南
Many KS3 CIE chemistry questions ask you to explain how a catalyst speeds up a reaction. To gain full marks, you must use precise scientific language from the mark scheme, such as ‘lowers activation energy’ and ‘not used up’. This article breaks down the key ideas and shows you how to write answers that examiners reward.
许多 KS3 CIE 化学试题要求你解释催化剂如何加快反应。要获得满分，你必须使用评分标准中的准确科学术语，例如 “降低活化能” 和 “不会被消耗”。本文将拆解这些关键概念，并教你如何写出考官认可的标准答案。
1. What a Catalyst Is | 什么是催化剂
A catalyst is a substance that increases the rate of a chemical reaction without being used up or permanently changed by the end of the reaction. It works by providing an alternative reaction pathway with a lower activation energy.
催化剂是一种能加快化学反应速率，但在反应结束时不会被消耗或发生永久性变化的物质。它通过提供一条活化能更低的可替代反应路径来起作用。
In the CIE mark scheme, you are often expected to write that a catalyst ‘speeds up a reaction’ and ‘remains unchanged in mass and chemical properties’. Avoid saying it ‘helps the reaction’ or ‘makes the reaction happen’ because these phrases are too vague.
在 CIE 评分标准中，通常要求你写出催化剂 “加快反应速率” 并且 “质量和化学性质保持不变”。避免使用 “帮助反应” 或 “使反应发生” 这类过于模糊的说法。
2. Activation Energy and Reaction Pathways | 活化能与反应路径
For a reaction to occur, reactant particles must collide with enough energy to break existing bonds and form new ones. The minimum energy required for a successful collision is called the activation energy, Eₐ.
要使反应发生，反应物粒子必须以足够的能量碰撞，从而断裂原有化学键并形成新键。成功碰撞所需的最低能量称为活化能 Eₐ。
A catalyst lowers the activation energy by offering a different route for the reaction. This does not increase the temperature or give particles extra energy; it simply allows more collisions to be successful at the same temperature.
催化剂通过提供不同的反应路径来降低活化能。它并不会升高温度或给粒子额外能量；它只是让更多碰撞在相同温度下能够成功。
Because a greater proportion of particles now have energy equal to or greater than the lowered Eₐ, the frequency of successful collisions increases, and the reaction rate increases.
由于现在有更大比例的粒子具有等于或高于降低后 Eₐ 的能量，成功碰撞的频率增加，反应速率随之加快。
3. How Catalysts Speed Up Reactions | 催化剂如何加快反应
The rate of a reaction depends mainly on how often particles collide with sufficient energy. A catalyst increases the rate by lowering the energy barrier, not by increasing the number of particles or their average kinetic energy.
反应速率主要取决于粒子以足够能量碰撞的频率。催化剂通过降低能量壁垒来提高速率，而不是增加粒子数量或它们的平均动能。
Even at KS3 level, examiners expect you to connect the lower activation energy to ‘more frequent successful collisions’. If you only say ‘it lowers activation energy’, you may get some credit, but adding the collision link often gains full marks.
即使在 KS3 阶段，考官也希望你将 “较低活化能” 与 “更频繁的成功碰撞” 联系起来。如果你只说 “它降低活化能”，可能会得到部分分数，但加上碰撞联系通常能获得满分。
For example, in the decomposition of hydrogen peroxide, adding manganese dioxide allows oxygen gas to be produced much faster, although the same products are formed overall.
例如，在过氧化氢分解中，加入二氧化锰会使氧气产生得更快，但最终生成的产物种类不变。
4. Catalysts Are Not Used Up | 催化剂不会被消耗
A catalyst may take part in intermediate steps during the reaction, but it is regenerated by the end. Therefore, its mass and chemical identity stay the same. This is a key mark scheme point.
催化剂可能在反应过程中参与中间步骤，但反应结束时会被再生。因此，它的质量和化学性质保持不变。这是评分标准中的关键得分点。
Students sometimes write that a catalyst ‘is not involved’ in the reaction. This is not precise, because catalysts are involved temporarily. The correct idea is that the catalyst is ‘not used up’ or ‘not permanently changed’.
有些学生会写催化剂 “不参与” 反应。这并不准确，因为催化剂会暂时参与。正确的表述是催化剂 “不会被消耗” 或 “不会发生永久性变化”。
In a marks scheme answer, you can also say ‘the catalyst can be recovered at the end of the reaction’. This demonstrates that it has not been chemically used up.
在评分标准答案中，你还可以写 “催化剂可以在反应结束后回收”。这表明它没有被化学消耗。
5. Enzymes as Biological Catalysts | 酶作为生物催化剂
Enzymes are biological catalysts found in living organisms. They speed up reactions such as digestion and respiration by lowering the activation energy, just like chemical catalysts do.
酶是存在于生物体内的生物催化剂。它们与化学催化剂一样，通过降低活化能来加快消化和呼吸等反应。
At KS3, you should know that enzymes are proteins and each enzyme is specific to one type of substrate. They work best at an optimum temperature and pH, and high temperatures can denature them.
在 KS3 阶段，你应该知道酶是蛋白质，每种酶对一种类型的底物具有特异性。它们在最适温度和 pH 下活性最高，高温会使它们变性。
Although enzymes are more complex, CIE questions often use them as an example of catalysts. The same mark scheme keywords still apply: lower activation energy, speed up reaction, and unchanged at the end.
尽管酶更为复杂，但 CIE 试题常将其作为催化剂的例子。同样的评分标准关键词仍然适用：降低活化能、加快反应速率、反应结束时保持不变。
6. Common Examples of Catalysts | 常见催化剂实例
Several examples appear regularly in KS3 CIE questions. Manganese dioxide (MnO₂) catalyses the decomposition of hydrogen peroxide (H₂O₂) into water and oxygen.
有几个例子经常出现在 KS3 CIE 试题中。二氧化锰（MnO₂）催化过氧化氢（H₂O₂）分解为水和氧气。
Platinum and rhodium in catalytic converters speed up the conversion of toxic gases such as carbon monoxide into less harmful carbon dioxide. Iron is used as a catalyst in the Haber process to make ammonia.
催化转化器中的铂和铑能加快有毒气体（如一氧化碳）转化为危害较小的二氧化碳。铁在哈伯制氨法中用作催化剂。
In biology, the enzyme catalase speeds up the breakdown of hydrogen peroxide in cells, protecting them from damage. Remembering these examples can help you recognise catalyst questions in
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