Catalysts – IGCSE CIE Chemistry | IGCSE CIE 化学：催化 考点精讲

📚 Catalysts – IGCSE CIE Chemistry | IGCSE CIE 化学：催化 考点精讲

Catalysts play a crucial role in chemical reactions by increasing the rate without being consumed. In IGCSE CIE Chemistry, understanding catalysts – their definition, how they work, and their real-world applications – is essential for explaining industrial processes and laboratory reactions. This article breaks down every key point you need to master for the exam, from activation energy to catalytic converters and specific industrial examples.

催化剂通过加快反应速率且自身不被消耗而在化学反应中扮演着关键角色。在IGCSE CIE化学中，理解催化剂——包括其定义、工作原理以及实际应用——对于解释工业流程和实验室反应至关重要。本文逐一梳理考试需要掌握的所有重点，从活化能到催化转化器，再到具体的工业实例。

1. What is a Catalyst? | 什么是催化剂？

A catalyst is a substance that increases the rate of a chemical reaction but remains chemically unchanged at the end of the reaction. It is not used up and can be recovered in the same mass as at the start.

催化剂是一种能够加快化学反应速率，但在反应结束时自身化学性质保持不变的物质。它不会被消耗掉，反应结束后可以以与开始时相同的质量被回收。

Catalysts work by providing an alternative reaction pathway with a lower activation energy. They do not alter the energy of the reactants or products, nor do they change the enthalpy change (ΔH) of the reaction.

催化剂通过提供一条具有较低活化能的替代反应途径来发挥作用。它们不会改变反应物或生成物的能量，也不会改变反应的焓变（ΔH）。

2. How Catalysts Work | 催化剂的工作原理

The key idea is that catalysts lower the activation energy (Eₐ) required for a reaction to occur. By reducing the energy barrier, a greater proportion of particles have energy equal to or greater than Eₐ, leading to a higher frequency of successful collisions.

关键概念是催化剂降低了反应发生所需的活化能（Eₐ）。通过降低能量壁垒，更大比例的粒子具有等于或高于Eₐ的能量，从而增加了有效碰撞的频率。

Catalysts provide an alternative pathway that may involve forming intermediate compounds with the reactants. These intermediates then break down to give the products and regenerate the catalyst. This mechanism allows the reaction to proceed more quickly while the catalyst remains unchanged overall.

催化剂提供一条可能涉及与反应物形成中间化合物的替代途径。这些中间体随后分解生成产物并再生催化剂。这一机理使得反应能够更快进行，而催化剂总体上保持不变。

3. Activation Energy and Reaction Pathway | 活化能与反应途径

Activation energy is the minimum energy colliding particles must possess for a reaction to happen. Without a catalyst, many reactions have a high Eₐ and proceed very slowly at room temperature.

活化能是碰撞粒子发生反应所必须具备的最低能量。没有催化剂的话，许多反应具有较高的Eₐ，在室温下进行得非常缓慢。

On an energy profile diagram, the presence of a catalyst is shown by a lower ‘hump’ for the activation energy. The enthalpy change (ΔH) remains the same, showing that the catalyst does not affect the overall energy change between reactants and products.

在能量分布图中，催化剂的存在表现为活化能的“峰”更低。焓变（ΔH）保持不变，这表明催化剂不影响反应物和生成物之间的总能量变化。

Eₐ (uncatalysed) > Eₐ (catalysed) ; ΔH unchanged

4. Types of Catalysts | 催化剂的类型

Catalysts can be divided into two broad categories: homogeneous and heterogeneous. A homogeneous catalyst is in the same phase (state) as the reactants, while a heterogeneous catalyst is in a different phase.

催化剂可分为两大类：均相催化剂和非均相催化剂。均相催化剂与反应物处于同一相态，而非均相催化剂则处于不同的相态。

In IGCSE, most examples are heterogeneous catalysts – typically solid catalysts used with gaseous or liquid reactants. For instance, iron in the Haber process and vanadium(V) oxide in the Contact process are solid catalysts operating with gases.

在IGCSE中，大多数例子是非均相催化剂——通常是固体催化剂与气体或液体反应物一起使用。例如，哈伯法中的铁和接触法中的五氧化二钒都是与气体反应的固体催化剂。

Homogeneous catalysts include enzymes in aqueous solutions, which are also part of the syllabus.

均相催化剂包括水溶液中的酶，这也属于考纲范围。

5. Enzymes – Biological Catalysts | 酶——生物催化剂

Enzymes are protein molecules that act as catalysts in living organisms. They are highly specific, each enzyme catalysing only one type of reaction or a small group of related reactions.

酶是在生物体内起催化作用的蛋白质分子。它们具有高度专一性，每种酶只催化一种类型或一小类相关的反应。

Enzymes work by the ‘lock and key’ model, where the substrate fits into the active site of the enzyme. This lowers the activation energy for the biological reaction, allowing processes such as digestion and respiration to occur at body temperature.

酶通过“锁钥”模型发挥作用，底物嵌入酶的活性位点。这降低了生物反应的活化能，使得消化和呼吸等过程能在体温下进行。

Typical IGCSE examples include the use of yeast (containing the enzyme zymase) to ferment glucose into ethanol, and the enzyme catalase breaking down hydrogen peroxide.

典型的IGCSE例子包括利用酵母（含有酒化酶）将葡萄糖发酵成乙醇，以及过氧化氢酶分解过氧化氢。

6. Catalytic Converters | 催化转化器

Catalytic converters in car exhaust systems use a mix of platinum, palladium, and rhodium as heterogeneous catalysts. They convert harmful gases into less harmful substances before they are released into the atmosphere.

汽车排气系统中的催化转化器使用铂、钯和铑的混合物作为非均相催化剂。它们在有害气体排放到大气之前将其转化为危害较小的物质。

The reactions catalysed include: oxidation of carbon monoxide to carbon dioxide (2CO + O₂ → 2CO₂), oxidation of unburnt hydrocarbons to CO₂ and H₂O, and reduction of nitrogen oxides to nitrogen and oxygen (2NO → N₂ + O₂; 2NO₂ → N₂ + 2O₂).

被催化的反应包括：一氧化碳氧化成二氧化碳（2CO + O₂ → 2CO₂），未燃烧的碳氢化合物氧化成CO₂和H₂O，以及氮氧化物还原成氮气和氧气（2NO → N₂ + O₂；2NO₂ → N₂ + 2O₂）。

This application is a classic IGCSE question linking catalysts, environmental chemistry, and redox reactions.

这一应用是IGCSE中将催化剂、环境化学和氧化还原反应联系起来的经典考题。

7. Industrial Example: Haber Process (Iron) | 工业实例：哈伯法（铁）

The Haber process manufactures ammonia (NH₃) from nitrogen and hydrogen: N₂ + 3H₂ ⇌ 2NH₃. The catalyst used is finely divided iron, which provides a large surface area for the reaction.

哈伯法由氮气和氢气制取氨（NH₃）：N₂ + 3H₂ ⇌ 2NH₃。所用催化剂是细碎的铁，为反应提供了大的表面积。

Without the iron catalyst, the reaction would be far too slow at the temperature used (around 450 °C). The catalyst lowers the activation energy, allowing a reasonable rate of production without using excessively high temperatures that would reduce yield (as the forward reaction is exothermic).

如果没有铁催化剂，在所用温度（约450°C）下反应会过于缓慢。催化剂降低了活化能，使得生产过程能保持合理的速率，而无需采用会降低产率（因为正反应放热）的过高温度。

Exam tip: Remember that the catalyst does not affect the position of equilibrium; it only helps the system reach equilibrium faster.

考试提示：记住催化剂不影响平衡位置；它只帮助体系更快达到平衡。

8. Industrial Example: Contact Process (Vanadium(V) Oxide) | 工业实例：接触法（五氧化二钒）

The Contact process produces sulfuric acid via the oxidation of sulfur dioxide to sulfur trioxide: 2SO₂ + O₂ ⇌ 2SO₃. The catalyst is vanadium(V) oxide, V₂O₅.

接触法通过将二氧化硫氧化为三氧化硫来生产硫酸：2SO₂ + O₂ ⇌ 2SO₃。催化剂是五氧化二钒，V₂O₅。

V₂O₅ provides an alternative pathway, forming intermediate compounds with SO₂ and O₂, thereby lowering the activation energy. This allows the reaction to occur efficiently at around 450 °C. Again, higher temperatures would harm the equilibrium yield but speed up the reaction; the catalyst resolves this trade-off.

V₂O₅提供了一条替代途径，与SO₂和O₂形成中间化合物，从而降低活化能。这使得反应能在约450°C下高效进行。同样，更高的温度会降低平衡产率但加快反应速率；催化剂解决了这一权衡问题。

This is often compared with the Haber process to highlight how different catalysts are chosen for different reactions based on their ability to adsorb reactants and weaken bonds.

这一点常与哈伯法作比较，突显如何根据不同催化剂的吸附反应物和削弱化学键的能力为不同反应选择催化剂。

9. Laboratory Example: Decomposition of Hydrogen Peroxide (Manganese(IV) Oxide) | 实验室实例：过氧化氢分解（二氧化锰）

The decomposition of hydrogen peroxide (H₂O₂ → 2H₂O + O₂) is slow at room temperature but becomes vigorous when manganese(IV) oxide, MnO₂, is added. MnO₂ acts as a heterogeneous catalyst.

过氧化氢的分解（H₂O₂ → 2H₂O + O₂）在室温下很慢，但加入二氧化锰（MnO₂）后反应变得剧烈。MnO₂充当非均相催化剂。

This experiment is frequently used in the IGCSE laboratory to investigate the effect of a catalyst. The rate of oxygen production can be measured, and MnO₂ can be filtered off and reused, proving it is chemically unchanged.

该实验在IGCSE实验室中常被用来探究催化剂的影响。可以测量氧气的生成速率，且MnO₂能过滤回收并重复使用，证明其化学性质不变。

Other substances like liver (containing catalase) or potassium iodide can also catalyse this reaction, offering a comparison of different types of catalysts.

其他物质如肝脏（含有过氧化氢酶）或碘化钾也能催化该反应，可对比不同类型的催化剂。

10. Hydrogenation of Alkenes (Nickel) | 烯烃加氢（镍）

In organic chemistry, the addition of hydrogen to an alkene (hydrogenation) requires a nickel catalyst. For example, ethene reacts with hydrogen to form ethane: C₂H₄ + H₂ → C₂H₆, using nickel at about 150 °C.

在有机化学中，烯烃加氢（氢化）需要镍催化剂。例如，乙烯与氢气反应生成乙烷：C₂H₄ + H₂ → C₂H₆，使用镍并在约150°C下进行。

The nickel catalyst provides a surface where hydrogen molecules and alkene molecules are adsorbed. This weakens the H–H bond and the C=C bond, allowing the atoms to rearrange more easily into the saturated product.

镍催化剂提供了一个表面，使氢分子和烯烃分子被吸附。这削弱了H–H键和C=C键，使得原子更容易重排形成饱和产物。

This process is used industrially to convert liquid vegetable oils (unsaturated) into solid margarine (saturated fats) by partial hydrogenation.

该过程在工业上用于通过部分加氢将液态植物油（不饱和）转化为固态人造黄油（饱和脂肪）。

11. Catalysts and Equilibrium | 催化剂与平衡

A common misconception is that catalysts increase the yield of a reversible reaction. In fact, a catalyst has no effect on the position of equilibrium. It speeds up both the forward and reverse reactions equally.

一个常见的误解是催化剂能提高可逆反应的产率。事实上，催化剂对平衡位置没有影响。它同等地加快正反应和逆反应的速率。

Because both rates increase by the same factor, equilibrium is reached faster, but the concentrations of reactants and products at equilibrium remain unchanged. The only way to alter the equilibrium position is to change temperature, pressure, or concentration.

由于两个方向的速率以相同的倍数增加，平衡能更快达到，但平衡时反应物和生成物的浓度保持不变。改变平衡位置的唯一方法是改变温度、压力或浓度。

Exam questions frequently test this point, especially in the context of the Haber and Contact processes, where temperature and pressure are chosen to optimise rate and yield together with the catalyst.

考试题目经常考察这一点，特别是在哈伯法和接触法的情境中，此时温度和压力的选择需要结合催化剂同时优化速率和产率。

12. Importance of Catalysts in Industry | 催化剂在工业中的重要性

Catalysts are vital in modern chemical industry for economic and environmental reasons. By lowering the temperature needed for a reaction, they save energy and reduce costs. They also allow processes to run at a faster rate, increasing productivity.

催化剂在现代化学工业中因经济和环境原因而至关重要。通过降低反应所需的温度，它们节约了能源并降低了成本。它们还使生产过程能以更快的速率运行，从而提高生产力。

From the Haber process providing fertilisers to catalytic converters reducing pollution, catalysts enable sustainable chemical manufacturing. Understanding their properties and mechanisms is therefore a core part of IGCSE chemistry and a favourite topic for structured questions.

从提供肥料的哈伯法到减少污染的催化转化器，催化剂使可持续的化学品生产成为可能。因此，理解它们的性质与机理是IGCSE化学的核心内容，也是结构化问题的热门主题。

Published by TutorHao | Chemistry Revision Series | aleveler.com

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