Reaction Rates | 反应速率考点精讲

📚 Reaction Rates | 反应速率考点精讲

Understanding the speed of chemical reactions is a fundamental part of chemistry. Whether it is rust forming slowly on a gate or an explosion happening in a split second, reaction rates can vary enormously. In the IGCSE CCEA Chemistry specification, you need to be able to define rate of reaction, explain how different factors affect it, and describe practical methods for measuring it. This article will guide you through every key point, using collision theory as the central explanatory model.

理解化学反应进行的快慢是化学的基础。无论是大门上铁锈慢慢形成，还是刹那间发生的爆炸，反应速率千差万别。在 IGCSE CCEA 化学的考试大纲中，你需要能够定义反应速率，解释不同因素如何影响它，并描述测量速率的实验方法。本文将以碰撞理论作为核心解释模型，带你梳理每一个重点。

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

The rate of a chemical reaction tells us how quickly reactants are converted into products. It is usually measured as the change in amount of a reactant or product per unit time. If a reactant is being used up, its amount is decreasing, so the rate can be expressed as a positive value using a minus sign in the equation.

化学反应速率告诉我们反应物转变为产物的快慢。通常用它来表示单位时间内反应物或产物量的变化。如果反应物被消耗，其量在减少，那么可以在方程中加上负号，使速率表示为正值。

Rate = Change in quantity of reactant or product / Time taken

速率 = 反应物或产物的量变化 / 所用时间

The quantity can be measured in terms of mass, volume of gas, concentration, or any property linked to the amount of substance. Typical units are g/s (grams per second), cm³/s, mol/dm³/s, or any appropriate combination.

量的变化可以用质量、气体的体积、浓度或任何与物质的量相关的性质来测量。常用的单位有 g/s (克每秒)、cm³/s、mol/dm³/s 等合适的组合。

2. Collision Theory | 碰撞理论

For a chemical reaction to occur, particles (atoms, molecules or ions) must collide. Collision theory states that a reaction will only take place when particles collide with the correct orientation and with a minimum amount of energy, called the activation energy. If these conditions are not met, the particles simply bounce off each other without reacting.

要发生化学反应，微粒（原子、分子或离子）必须发生碰撞。碰撞理论指出，只有当微粒以正确的取向发生碰撞，并且具有的最低能量达到活化能时，反应才会发生。如果这些条件没有满足，微粒只是彼此弹开，不会发生反应。

The rate of reaction therefore depends on how often successful collisions occur per second – known as the frequency of successful collisions. Any change that increases the number of successful collisions per second will increase the rate.

因此，反应速率取决于每秒钟发生有效碰撞的频率，即有效碰撞频率。任何能使每秒有效碰撞次数增加的变化，都会使反应速率加快。

3. Activation Energy | 活化能

Activation energy (Eₐ) is the minimum energy that colliding particles must have before a reaction can happen. It can be thought of as an energy barrier. Even if particles collide with the correct orientation, if their combined kinetic energy is less than Eₐ, they will not react. Activation energy is different for different reactions.

活化能 (Eₐ) 是碰撞粒子发生反应前所必须具备的最低能量。它可被视为一个能垒。即使粒子以正确的取向碰撞，如果它们的总动能小于活化能，也不会反应。不同反应的活化能各不相同。

On an energy profile diagram, Eₐ is the difference in energy between the reactants and the highest point on the curve (the transition state). A low Eₐ means a fast reaction; a high Eₐ means a slow reaction under the same conditions.

在能量变化示意图中，活化能是从反应物到曲线最高点（过渡态）之间的能量差值。活化能低意味着反应快；在相同条件下，活化能高则反应慢。

4. Effect of Concentration on Rate | 浓度对反应速率的影响

Increasing the concentration of reactants in a solution means there are more particles dissolved in a given volume. This makes the particles closer together and increases the frequency of collisions. Since more collisions occur per second, there are more successful collisions per second, so the rate of reaction increases.

增大溶液中反应物的浓度，意味着在给定体积中溶解了更多的粒子。这使得粒子更靠近，提高了碰撞频率。由于每秒发生的碰撞更多，每秒有效碰撞的次数也随之增加，因此反应速率加快。

This can be demonstrated by reacting marble chips (calcium carbonate) with hydrochloric acid of different concentrations, measuring the volume of carbon dioxide gas produced over time. The steeper the initial slope of the gas-volume-time graph, the faster the rate.

这可以通过用不同浓度的盐酸与大理石碎片（碳酸钙）反应，测量一段时间内产生的二氧化碳气体体积来验证。气体体积–时间图的初始斜率越陡，表示速率越快。

Higher concentration → more particles per unit volume
浓度越大 → 单位体积粒子数越多
More frequent collisions → higher frequency of successful collisions
碰撞更频繁 → 有效碰撞频率更高
Rate increases proportionally for many simple reactions
对许多简单反应而言，速率近似成正比增加

5. Effect of Pressure on Rate (for Gases) | 压强对气体反应速率的影响

For reactions involving gases, increasing the pressure at constant temperature compresses the gas into a smaller volume. This has the same effect as increasing the concentration: there are more gas particles per unit volume. Collisions become more frequent, so the rate of reaction increases.

对于有气体参加的反应，在恒定温度下增大压强，会把气体压缩到更小的体积中。这和增大浓度的效果相同：单位体积内的气体粒子数增多。碰撞变得更频繁，因此反应速率加快。

When you are asked about the effect of pressure, remember that the explanation mirrors the effect of concentration but applies specifically to gases. Decreasing pressure has the opposite effect – the rate decreases.

当被问及压强的影响时，记住其解释与浓度的影响类似，但专门针对气体。降低压强则效果相反——速率减慢。

6. Effect of Temperature on Rate | 温度对反应速率的影响

Raising the temperature increases the rate of reaction dramatically. There are two reasons for this. First, particles have more kinetic energy and move faster, so they collide more often. This increases the frequency of collisions. Second, and more importantly, a greater proportion of the particles now have energy equal to or greater than the activation energy. This causes a huge increase in the frequency of successful collisions.

升高温度会显著加快反应速率。原因有二。首先，粒子具有更大的动能，运动更快，因此碰撞更频繁，提高了碰撞频率。其次，更重要的是，此时有更大比例的粒子具有等于或大于活化能的能量。这使得有效碰撞的频率急剧增加。

Even a small temperature rise of 10 °C can roughly double the rate of many reactions. This is mainly due to the large increase in the number of particles exceeding the activation energy, not simply the increase in collision frequency.

即便温度仅仅上升 10 °C，许多反应的速率大约也会加倍。这主要是因为超越活化能的粒子数目大幅增加，而不仅仅是碰撞频率的提高。

7. Effect of Surface Area on Rate | 表面积对反应速率的影响

If a solid reactant is broken into smaller pieces, its total surface area increases while its mass remains the same. A larger surface area means more particles are exposed and available for collisions at the same time. This increases the frequency of collisions and therefore the rate of reaction.

如果将固体反应物打碎成更小的块状，其总表面积增加，而质量不变。更大的表面积意味着在同一时间有更多粒子暴露出来，可供碰撞。这提高了碰撞频率，从而加快反应速率。

A classic investigation is comparing the reaction of a large marble chip with hydrochloric acid against the same mass of powdered marble. The powder produces gas much faster, and the graph of gas volume against time shows a steeper initial slope for the powder.

一个经典的探究实验是比较大块大理石与等质量的大理石粉末跟盐酸的反应。粉末产生气体的速度快得多，气体体积–时间图上粉末的初始斜率更陡。

Smaller particles → larger surface area
颗粒越小 → 表面积越大
More exposed particles → more frequent collisions
暴露的粒子越多 → 碰撞更频繁
Rate increases significantly
速率显著提高

8. Effect of Catalysts on Rate | 催化剂对反应速率的影响

A catalyst is a substance that increases the rate of a chemical reaction without being chemically changed or used up itself. Catalysts work by providing an alternative reaction pathway with a lower activation energy. Because the energy barrier is lower, a much greater proportion of particles have enough energy to react when they collide, so the frequency of successful collisions increases sharply.

催化剂是一种能加快化学反应速率、而自身在化学上不发生改变、不被消耗的物质。催化剂通过提供一条活化能较低的其他反应途径来起作用。由于能垒降低，有更高比例的粒子在碰撞时具有足够能量发生反应，因此有效碰撞频率急剧增加。

A catalyst does not alter the energy of reactants or products, nor does it affect the overall energy change (ΔH). It simply lowers the activation energy, making the reaction faster. In an energy profile diagram, the hump is lower for the catalysed route.

催化剂不会改变反应物或产物的能量，也不影响总能量变化 (ΔH)。它只是降低了活化能，使反应变快。在能量变化示意图中，有催化剂参与的那条路径对应的峰高较低。

Enzymes are biological catalysts that work in living organisms. They are highly specific, often operating under mild conditions of temperature and pH, and play vital roles in processes such as digestion and respiration.

酶是生物体内的催化剂。它们高度专一，通常在温和的温度和pH条件下发挥作用，在消化和呼吸等过程中起着至关重要的作用。

9. Measuring Rates of Reaction Experimentally | 通过实验测量反应速率

You must be able to describe how the rate of a reaction can be followed by measuring changes in mass, gas volume, colour or turbidity. The choice of method depends on the nature of the reaction.

你必须能够描述如何通过测量质量、气体体积、颜色或浊度的变化来跟踪反应速率。方法的选择取决于反应的性质。

Method 方法	Typical reaction 典型反应	What is measured 测量量
Mass loss 质量损失	Marble chips + acid (CO₂ released) 大理石+酸(释放CO₂)	Decrease in mass as gas escapes 气体逸出导致质量减少
Gas volume 气体体积	Hydrogen peroxide decomposition (O₂) 过氧化氢分解(产生O₂)	Volume of gas collected in a syringe or measuring cylinder 用注射器或量筒收集的气体体积
Colour change 颜色变化	Sodium thiosulfate + HCl (precipitate forms) 硫代硫酸钠+盐酸(生成沉淀)	Time for a cross to disappear under conical flask 锥形瓶下十字消失的时间
Turbidity 浊度	Same as above 同上	Decrease in light passing through (using a data logger) 光透过率下降(用数据采集器)

In each case, the rate can be found by recording a measurable property against time and then calculating the gradient of the graph at the desired point. For an average rate, you can use the total change divided by the total time.

在每一种方法中，记录某一可测量的性质随时间的变化，然后计算所需点处图线的斜率，即可求得速率。要计算平均速率，可以用总变化量除以总时间。

10. Interpreting Rate Graphs and Maxwell-Boltzmann Distribution | 解释速率图与麦克斯韦–玻尔兹曼分布

When you plot the quantity of product formed (or reactant used up) against time, the slope tells you the rate. A steep slope means a fast rate; a curve that becomes less steep shows the rate slowing down as reactants are used up.

当你绘制生成产物量（或消耗反应物量）随时间变化的图像时，斜率代表速率。陡峭的斜率意味着速率快；曲线逐渐变缓说明随着反应物消耗，速率减慢。

The Maxwell-Boltzmann distribution shows the spread of kinetic energies among particles in a gas or liquid at a given temperature. The curve starts at the origin, peaks, and then tails off at high energies. Only the particles to the right of the activation energy line have sufficient energy to react. The area under the curve beyond Eₐ represents the number of particles with enough energy to react.

麦克斯韦–玻尔兹曼分布显示了在给定温度下，气体或液体中微粒的动能分布。曲线从原点开始，达到峰值后在高能区逐渐拖尾。只有处于活化能线右侧的粒子才具有足够的能量发生反应。活化能线以外的曲线下面积代表了具有足够能量发生反应的粒子数。

When temperature is increased, the distribution curve flattens and shifts to the right, with a much bigger area beyond Eₐ. This explains why a small temperature rise causes a large increase in rate. A catalyst, on the other hand, does not change the distribution; instead it moves the activation energy line to the left (lower Eₐ), so a much larger area of the curve now lies to the right of the new barrier.

温度升高时，分布曲线变得扁平并向右移动，超过活化能的面积大大增加。这就解释了为什么小幅升温会造成速率的大幅提高。而催化剂并不改变分布曲线，而是将活化能线向左移（降低Eₐ），使曲线在新能垒右侧的面积大幅增加。

Be ready to sketch and interpret the Maxwell-Boltzmann curve for both temperature and catalyst effects in CCEA exam questions.

在 CCEA 考试中，要准备好绘制并解释温度与催化剂影响下的麦克斯韦–玻尔兹曼曲线。

Published by TutorHao | Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Reaction Rates | 反应速率 考点精讲