Rates of Reaction: An Edexcel IGCSE Science Revision Guide | 化学反应速率：爱德思 IGCSE 科学备考指南

📚 Rates of Reaction: An Edexcel IGCSE Science Revision Guide | 化学反应速率：爱德思 IGCSE 科学备考指南

In Edexcel IGCSE Chemistry and the Science (Double Award) specification, the study of reaction rates appears in the physical chemistry section. You need to be able to define rate, describe experiments, explain collision theory and analyse graphs. This guide follows the language and type of explanation that examiners reward.

在爱德思 IGCSE 化学与科学（双奖）大纲中，反应速率属于物理化学部分。你需要能够定义速率、描述实验、解释碰撞理论并分析曲线图。本指南采用考官认可的语言和解释方式，帮助你在考试中稳稳拿分。

1. What Is Rate of Reaction? | 什么是反应速率？

The rate of a reaction tells us how quickly a reactant is used up or how quickly a product is formed. In the laboratory we measure this by following a change in mass, a volume of gas, or a change in colour or turbidity.

反应速率告诉我们反应物被消耗得快还是产物生成得快。在实验室里，我们通过测量质量变化、气体体积或颜色/浑浊度的变化来追踪它。

rate = amount of reactant used up ÷ time taken

rate = amount of product formed ÷ time taken

Rates are usually expressed in units such as g/s, cm³/s, mol/s or 1/s (for turbidity). You do not need to memorise every unit, but you should be able to choose the correct unit for the measuring method used.

速率常用单位包括 g/s、cm³/s、mol/s 或 1/s（用于浑浊度）。你不需要背下所有单位，但应该能为所用测量方法选出合适的单位。

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2. How to Measure Reaction Rate | 如何测量反应速率

There are four standard experiments you should be ready to describe:

有四个标准实验你需要会描述：

• Gas collection. A gas syringe is attached to the reaction flask. The volume of gas is recorded at fixed time intervals. This is used for reactions such as magnesium with hydrochloric acid, producing hydrogen.

  气体收集法：将气针筒连接到反应烧瓶上，每隔固定时间记录气体体积。例如镁与盐酸反应生成氢气。

• Loss of mass. The flask is placed on a balance. If a gas escapes, the total mass decreases. A small plug of cotton wool prevents acid spray while allowing gas to leave. This works well for the reaction of calcium carbonate with hydrochloric acid, producing carbon dioxide.

  质量减少法：把烧瓶放在天平上。如果有气体逸出，总质量会下降。塞一小团棉花可以阻止酸液溅出，同时让气体逸出。这个方法适用于碳酸钙与盐酸生成二氧化碳的反应。

• Disappearing cross. A flask containing sodium thiosulfate solution is placed on a piece of paper with a cross drawn on it. Hydrochloric acid is added and the time for the cross to disappear is measured. This measures the time taken for a fixed amount of sulfur precipitate to form.

  十字遮挡法：把装有硫代硫酸钠溶液的烧瓶放在画有十字的纸上，加入盐酸，测量十字刚好消失所需的时间。这样测量的是生成固定量硫沉淀所需的时间。

• Change in pH. For acid-base reactions, a pH meter or indicator can monitor how quickly the pH changes.

  pH 变化法：对于酸碱反应，可用 pH 计或指示剂监测 pH 变化的快慢。

If you are asked to “improve the experiment”, the most useful answer is to repeat readings and calculate a mean, or to use a data logger for more precise measurements.

如果被问到“如何改进实验”，最有用的答案是重复读数并计算平均值，或使用数据记录器获得更精确的测量结果。

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3. Collision Theory | 碰撞理论

For a reaction to happen, reactant particles must collide with each other. However, not every collision leads to a reaction. The particles must collide with enough energy to break existing bonds. This minimum energy is called the activation energy, Eₐ.

反应发生的前提是反应物粒子相互碰撞。但并非每次碰撞都会引发反应。粒子必须具有足够的能量来断裂原有化学键，这个最低能量称为活化能 Eₐ。

This is why the phrase “successful collision” is so important. A successful collision is one that has the correct geometry and enough energy to form products. Any factor that increases the number of successful collisions per second will increase the rate of reaction.

这就是为什么“有效碰撞”这个短语非常重要。有效碰撞是指方向合适、能量足够，能够生成产物的碰撞。任何能增加每秒钟有效碰撞次数的因素都会加快反应速率。

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4. Surface Area | 表面积

Increasing the surface area of a solid reactant exposes more particles to the other reactant. For example, powdered calcium carbonate reacts faster than large marble chips because the total surface area is much larger.

增大固体反应物的表面积，会使更多粒子暴露在另一种反应物中。例如，粉末状碳酸钙比大块大理石反应更快，因为总表面积大得多。

A smaller particle size means a higher surface area to volume ratio. The effect is that there are more frequent collisions between reactant particles per second, so the rate of reaction increases.

粒径更小意味着表面积与体积之比更大。其结果是每秒内反应物粒子的碰撞更加频繁，反应速率加快。

You should avoid saying that particles move faster. Surface area does not change the speed of particles; it changes the number of exposed particles, and therefore the frequency of collisions.

你应该避免说“粒子运动得更快”。表面积不会改变粒子运动速度，它改变的是暴露的粒子数量，因此改变碰撞频率。

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5. Concentration and Pressure | 浓度与压强

In a solution, increasing concentration means more solute particles are present in the same volume. The particles are closer together, so they collide more often. More collisions per second means more successful collisions per second, and the rate increases.

在溶液中，增大浓度意味着相同体积内有更多溶质粒子。粒子之间的距离更近，因此碰撞更频繁。每秒碰撞次数增加，每秒有效碰撞次数也增加，速率加快。

For gases, increasing pressure has the same effect because it decreases the volume available to the same number of particles, squeezing them together.

对于气体，增大压强也有同样效果，因为相同粒子数可占据的体积变小，粒子被压缩得更紧密。

A common exam statement is: “Concentration only affects the frequency of collisions, not the energy of the collisions.” This is true, and it is a useful phrase in long-answer questions.

一个常见考试表述是：“浓度只影响碰撞频率，不影响碰撞能量。”这是正确的，也是长答题中的有用表述。

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6. Temperature | 温度

When temperature increases, particles gain kinetic energy and move faster. More importantly, a greater proportion of particles now have energy greater than or equal to the activation energy. Therefore many more collisions are successful.

当温度升高时，粒子获得动能并运动得更快。更重要的是，现在有更大比例的粒子具有大于或等于活化能的能量。因此有效碰撞大大增加。

As a rough rule, many reactions double in rate for every 10 °C rise in temperature. The enthalpy change ΔH does not change because of temperature; that would be another mistake to avoid in the exam.

粗略地说，温度每升高 10 °C，许多反应的速率会翻倍。反应的焓变 ΔH 不会因温度改变而改变，这也是考试中要避免的错误。

Note: temperature increases both the frequency of collisions and the percentage of successful collisions, whereas concentration and surface area only increase the frequency.

注意：温度既增加碰撞频率，又增加有效碰撞比例；而浓度和表面积只增加碰撞频率。

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7. Catalysts | 催化剂

A catalyst is a substance that speeds up a reaction without being used up. It provides an alternative reaction route with a lower activation energy. This means that more particles have enough energy to react, so the rate increases.

催化剂是一种能加快反应速率但自身不被消耗的物质。它提供了活化能更低的新反应路径。这意味着更多粒子拥有足够能量去反应，从而加快速率。

Catalysts are very important in industry because they reduce the energy needed to make products. For example, an iron catalyst is used in the Haber process for making ammonia, and platinum is used in the contact process for sulfuric acid.

催化剂在工业上非常重要，因为它们能降低生产所需的能量。例如，哈伯法制氨使用铁催化剂，接触法制硫酸使用铂催化剂。

In an exam, do not say that a catalyst is “used up” or that it changes the products. A catalyst only changes the speed of the reaction, not the position of equilibrium or the yield at equilibrium.

在考试中，不要说催化剂“被消耗”或改变产物。催化剂只改变反应速率，不改变平衡位置或平衡产量。

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8. Reading Rate Graphs | 速率曲线图分析

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