Rates of Reaction: A Complete Revision Guide | 反应速率：完整复习指南

📚 Rates of Reaction: A Complete Revision Guide | 反应速率：完整复习指南

This article provides a focused revision guide for the topic of rates of reaction in Edexcel IGCSE Science (Chemistry). It covers definitions, measurement methods, the four main factors that affect how fast reactions proceed, and how to interpret rate graphs. By the end, you will be ready to answer exam questions with confidence.

本文为爱德思 IGCSE 科学（化学）中“反应速率”专题提供精准备考指南。内容包括定义、测量方法、影响反应快慢的四大因素以及如何解读速率曲线。学完本文，你将能够自信地回答相关考试题目。

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

The rate of a chemical reaction tells us how quickly a reactant is used up or a product is formed. It is an important idea because it helps us control industrial processes, understand biological enzymes, and even prevent harmful reactions. In Edexcel IGCSE, you need to be able to describe reactions in terms of decreasing mass, increasing gas volume, or colour changes.

化学反应速率告诉我们反应物被消耗或产物生成的快慢。这一概念非常重要，因为它能帮助我们控制工业过程、理解生物酶，甚至防止有害反应。在爱德思 IGCSE 中，你需要能够从质量减少、气体体积增大或颜色变化等方面来描述反应。

Common observable changes used to follow a reaction include:

Loss of mass if a gas escapes from the container.

若气体从容器中逸出，质量会减少。
Volume of gas produced, collected in a gas syringe or over water.

生成气体的体积，可通过气体注射器或排水集气法收集。
Appearance of a precipitate, measured as turbidity or cloudiness.

出现沉淀，可通过浑浊程度来测量。
Colour change of a solution, for example in redox reactions.

溶液颜色变化，例如在氧化还原反应中。

2. Measuring Rate | 测量速率

To measure a reaction rate, you choose one amount that changes with time and record how it changes over a short interval. The general equation is:

rate = change in amount / change in time

The amount can be measured in grams of mass lost, cubic centimetres of gas produced, or moles of product formed. Common units of rate include g/s, cm³/s and mol/s.

要测量反应速率，你需要选择一个随时间改变的量，并记录它在一段较短时间内的变化。通用公式为：

速率 = 物质的量变化 / 时间变化

物质的量可以是用克表示的质量损失、用立方厘米表示的气体体积或生成的摩尔数。常见的速率单位有 g/s、cm³/s 和 mol/s。

The two most common methods are measuring mass loss on a balance, and collecting the gas produced in a gas syringe. Mass loss is used when a gas is given off and the reaction container is open. Gas collection is used when you need the exact volume of gas at regular time intervals.

两种最常用的方法是在天平上测量质量损失，以及用气体注射器收集生成的气体。当反应放出气体且容器开放时使用质量损失法；当需要在固定时间间隔内获得准确气体体积时使用气体收集法。

3. Collision Theory | 碰撞理论

For a chemical reaction to occur, reactant particles must collide with each other. However, not every collision leads to a reaction. The particles must collide with enough energy to break the existing bonds and with the correct orientation so that the new bonds can form. The minimum energy needed for a successful collision is called the activation energy, Eₐ.

要使化学反应发生，反应物粒子必须相互碰撞。但并非每次碰撞都能引发反应。粒子必须具有足够的能量来断裂原有化学键，并且碰撞方向必须正确，新的化学键才能形成。发生有效碰撞所需的最低能量称为活化能，用 Eₐ 表示。

Any factor that increases the frequency of collisions or the proportion of successful collisions will increase the rate of reaction. This idea is the key to understanding why concentration, pressure, temperature, surface area and catalysts affect reaction speed.

任何能增加碰撞频率或有效碰撞比例的因素都会加快反应速率。这就是理解浓度、压强、温度、表面积和催化剂影响反应速度的关键。

4. Concentration and Pressure | 浓度和压强

Increasing the concentration of a solution means there are more reactant particles in the same volume. This results in a higher frequency of collisions between reactant particles, so the rate of reaction increases. For gases, increasing the pressure has the same effect: the particles are compressed into a smaller volume, making collisions more frequent.

增加溶液浓度意味着在相同体积内有更多反应物粒子。这会带来更高的粒子碰撞频率，从而使反应速率增大。对于气体而言，增大压强具有同样的效果：粒子被压缩到更小的体积中，碰撞更加频繁。

It is important to state that only reactants affect the rate; adding concentrated acid to a fixed amount of metal will speed up the reaction until the metal is used up. Do not say “more collisions are successful” unless you also mention that the collision energy distribution is unchanged. Concentration mainly increases the total number of collisions per second, and therefore the number of successful collisions per second.

需要特别说明的是，只有反应物的浓度会影响速率；向固定量的金属中加入更浓的酸会加快反应速率，直到金属被消耗完。不要只说“有效碰撞更多”，除非你同时指出能量分布并未改变。浓度主要增加的是每秒碰撞总数，因此也增加了每秒有效碰撞的次数。

5. Temperature | 温度

Temperature is often the most powerful factor affecting reaction rate. When the temperature increases, the particles gain more kinetic energy and move faster. This increases the collision frequency slightly, but the much more dramatic effect is that a greater proportion of particles have energy equal to or greater than the activation energy.

温度往往是影响反应速率最有力的因素。温度升高时，粒子获得更多动能并运动得更快。这会略微增加碰撞频率，但更显著的效果是，拥有等于或大于活化能的粒子比例大幅增加。

For many common reactions, a rise of 10 °C roughly doubles the rate. This is why food decays faster in warm weather and why chemical reactions are often carried out in heated water baths. In exam answers, always refer to “more particles with energy ≥ Eₐ” as well as “more collisions per second”.

对于许多常见反应来说，温度升高 10 °C 大约会使速率翻倍。这就是为什么食物在温暖天气中腐败更快，以及为什么化学反应常在加热水浴中进行。在考试作答中，一定要提到“更多粒子的能量 ≥ Eₐ”以及“每秒碰撞次数更多”。

6. Surface Area | 表面积

For solid reactants, only the particles at the surface are available for collisions with particles in a solution or gas. Breaking a large lump into smaller pieces, or grinding it into a powder, increases the total surface area. This exposes more reactant particles to potential collisions and therefore increases the frequency of collisions.

对于固体反应物，只有位于表面的粒子才能与溶液或气体中的粒子发生碰撞。将大块固体破碎成小块，或研磨成粉末，可以增大总表面积。这会暴露更多反应物粒子以供碰撞，从而增加碰撞频率。

In practical work, marble chips and hydrochloric acid react more quickly when the chips are small or powdered. The rate is also faster because the mass loss in the first minute will be greater for the powder. Surface area does not change the activation energy; it only changes how often particles meet.

在实验中，大理石碎片与盐酸的反应在小块或粉末状态下更快。原因在于粉末在第一分钟内的质量损失更大。表面积并不会改变活化能，它只改变粒子相遇的频率。

7. Catalysts | 催化剂

A catalyst is a substance that speeds up a reaction but is chemically unchanged at the end. It works by providing an alternative pathway with a lower activation energy. This means that at the same temperature, a much larger proportion of particles can successfully react. A catalyst does not increase the yield of a reaction, but it helps the reaction reach equilibrium faster.

催化剂是一种能加快反应速率，但反应结束后自身化学性质不变的物质。它通过提供一条活化能较低的替代途径来起作用。这意味着在相同温度下，有更大比例的粒子能够成功反应。催化剂不会提高反应产率，但能帮助反应更快达到平衡。

Common examples include manganese(IV) oxide for the decomposition of hydrogen peroxide, and iron in the Haber process for making ammonia. In industry, catalysts save energy because they allow reactions to be run at lower temperatures than would otherwise be possible.

常见的例子有过氧化氢分解时使用的二氧化锰，以及哈伯法制氨时使用的铁。在工业中，催化剂可以节约能源，因为它们允许反应在比原本所需更低的温度下进行。

8. Graphs and Rate Calculations | 图表与速率计算

Reaction rates are often investigated by plotting the volume of gas produced against time. The graph starts steep and gradually becomes flat, as reactants are used up and the rate falls to zero. The steeper the line, the faster the reaction.

反应速率通常通过绘制“气体体积对时间”的曲线来研究。曲线一开始很陡，然后逐渐变平，因为反应物被消耗，速率降至零。直线越陡，说明反应越快。

To calculate the average rate over a period, use:

average rate = final volume − initial volume / final time − initial time

To calculate the instantaneous rate at a particular time, draw a tangent to the curve at that time and find its gradient.

要计算某段时间内的平均速率，使用公式：

平均速率 =（最终体积 − 初始体积）/（最终时间 − 初始时间）

要计算某一时刻的瞬时速率，需要在该时刻画一条切线，并求出切线的斜率。

Consider the following data from an experiment in which hydrochloric acid reacts with calcium carbonate to produce carbon dioxide gas:

考虑以下实验数据：盐酸与碳酸钙反应生成二氧化碳气体。

Time / s	Volume of CO₂ / cm³
0	0
10	24
20	40
30	50
40	55

The average rate between 0 and 20 s is (40 − 0) / (20 − 0) = 2.0 cm³/s. Between 20 and 40 s it is (55 − 40) / (40 − 20) = 0.75 cm³/s. This shows the reaction slowing down.

0 到 20 秒之间的平均速率为（40 − 0）/（20 − 0）= 2.0 cm³/s。20 到 40 秒之间的平均速率为（55 − 40）/（40 − 20）= 0.75 cm³/s。这说明反应正在减慢。

9. Core Practical and Exam Tips | 核心实验与考试技巧

The Edexcel IGCSE core practical for rates often involves adding marble chips to dilute hydrochloric acid and measuring the volume of carbon dioxide released over time. You should know how to set up a gas syringe, why you use a constant temperature (e.g., a water bath), and how to control variables such as mass of marble and volume of acid.

爱德思 IGCSE 关于速率的核心实验通常是将大理石碎片加入稀盐酸，并在不同时间测量释放出的二氧化碳体积。你需要知道如何安装气体注射器、为什么要在恒定温度下进行（例如使用水浴），以及如何控制大理石质量和酸的体积等变量。

In exam answers, always link a factor to “successful collisions per second” rather than just “collisions”. For example: “Increasing the concentration increases the number of particles per unit volume, which increases the frequency of successful collisions, so the rate increases.” Include units in all calculations, and read the tangent line carefully when finding a gradient.

在考试作答中，始终要把因素与“每秒有效碰撞次数”联系起来，而不仅仅是“碰撞”。例如：“增大浓度会使单位体积内粒子数增加，从而增加有效碰撞频率，因此速率增大。”所有计算都要带上单位，在求切线斜率时要小心读数。

Remember that catalysts do not appear in the overall equation and are not consumed. They only lower the activation energy, so they speed up both the forward and reverse reactions equally in a reversible reaction.

请记住，催化剂不会出现在总反应方程式中，也不会被消耗。它们只降低活化能，因此在可逆反应中会同等程度地加快正反应和逆反应。

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Rates of Reaction: A Complete Revision Guide | 反应速率：完整复习指南