IGCSE Edexcel Chemistry: Rate of Reaction | IGCSE Edexcel 化学：反应速率 考点精讲

📚 IGCSE Edexcel Chemistry: Rate of Reaction | IGCSE Edexcel 化学：反应速率 考点精讲

The rate of a chemical reaction tells us how quickly reactants are turned into products. In IGCSE Edexcel Chemistry, understanding reaction rates involves measuring the speed of reactions, explaining them using collision theory, and predicting how changing conditions (concentration, temperature, surface area, catalysts) affects the rate. This article covers all key points, from definitions to graph interpretation, with paired English–Chinese explanations to help you revise efficiently.

化学反应速率说明反应物转化为产物的快慢。在 IGCSE Edexcel 化学中，理解反应速率涉及测量反应快慢、用碰撞理论解释，以及预测如何改变条件（浓度、温度、表面积、催化剂）影响速率。本文涵盖从定义到图表解读的所有考点，以中英对照讲解，帮助你高效复习。

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

The rate of a chemical reaction is the change in concentration of a reactant or product per unit time. It is usually expressed in mol dm⁻³ s⁻¹ for solutions, or g s⁻¹ or cm³ s⁻¹ for mass or volume changes.

化学反应速率是指单位时间内反应物或产物浓度的变化量。对溶液通常以 mol dm⁻³ s⁻¹ 表示，对质量或气体体积变化则用 g s⁻¹ 或 cm³ s⁻¹。

Rate can be determined by measuring how fast a reactant is used up or how fast a product is formed. The units depend on the measurement method.

速率可通过测量反应物消耗的速率或产物生成的速率来确定。单位取决于测量方法。

2. Measuring the Rate of Reaction | 测量反应速率

We can follow the progress of a reaction by monitoring a property that changes over time. Common methods include: measuring the volume of gas evolved, measuring the loss in mass, observing the time taken for a colour change, or monitoring the time for a precipitate to obscure a mark (turbidity).

我们可以通过监测随时间变化的某个性质来跟踪反应进程。常用方法包括：测量生成气体的体积、测量质量减少、观察颜色变化所需的时间，或监测沉淀遮盖标记的时间（浊度法）。

• Gas volume: Use a gas syringe or an inverted measuring cylinder over water. Record the volume at fixed time intervals.
• 气体体积法：使用气体注射器或排水集气法。每隔固定时间记录体积。
• Mass loss: Place the reaction flask on a balance. As gas escapes, the mass decreases. Record mass against time.
• 质量减少法：将反应容器放在天平上。气体逸出时质量减少。记录质量随时间的变化。
• Colour change: Time how long it takes for a colour to appear or disappear, often using a stopwatch.
• 颜色变化：测定颜色出现或消失所需的时间，通常使用秒表。
• Turbidity (disappearing cross): For reactions producing a precipitate (e.g. sodium thiosulfate and hydrochloric acid), measure the time for a cross drawn on paper beneath the flask to disappear.
• 浊度法（消失的十字）：对于产生沉淀的反应（如硫代硫酸钠与盐酸），测量反应器下画在纸上的十字消失的时间。

The rate can be calculated as: Rate = Change in quantity / Time taken. For an average rate, use the total change and total time. For the rate at a specific moment, draw a tangent to the curve on a graph.

速率可计算为：速率 = 量的变化 / 所需时间。平均速率用总变化量和总时间。某一瞬间的速率则需在图上画切线求得。

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3. Collision Theory | 碰撞理论

Chemical reactions occur when particles (atoms, molecules, ions) collide with enough energy and with the correct orientation. This is called collision theory.

当粒子（原子、分子、离子）以足够的能量和正确的取向发生碰撞时，化学反应才会发生。这就是碰撞理论。

The minimum energy required for a successful collision is called the activation energy (Eₐ). If colliding particles have energy less than Eₐ, they simply bounce off without reacting.

发生有效碰撞所需的最小能量称为活化能 (Eₐ)。如果碰撞粒子的能量低于 Eₐ，它们只会弹开而不发生反应。

The rate of reaction depends on the number of successful collisions per unit time. More frequent successful collisions mean a faster reaction.

反应速率取决于单位时间内有效碰撞的次数。有效碰撞越频繁，反应越快。

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4. Factors Affecting Rate: Concentration | 影响速率的因素：浓度

Increasing the concentration of reactants in solution increases the rate of reaction. This is because there are more particles per unit volume, leading to more frequent collisions per unit time.

增大溶液中反应物的浓度可提高反应速率。这是因为单位体积内粒子数目增多，导致单位时间内碰撞更加频繁。

For gases, increasing the pressure has the same effect as increasing concentration: the particles are pushed closer together, increasing the frequency of collisions.

对于气体，增大压强与增大浓度效果相同：粒子被挤压得更近，碰撞频率增加。

The relationship is often directly proportional: doubling the concentration of a reactant approximately doubles the rate, provided the reactant appears in the rate-determining step (simple cases in IGCSE).

通常二者成正比关系：将反应物浓度加倍，速率也大约加倍（在 IGCSE 的简单情况下，假设该反应物参与速率控制步骤）。

Example: In the reaction between magnesium and hydrochloric acid, increasing the acid concentration speeds up the production of hydrogen gas.

示例： 镁与盐酸的反应中，增加酸浓度会加快氢气的生成。

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5. Factors Affecting Rate: Temperature | 影响速率的因素：温度

Increasing the temperature significantly increases the rate of reaction. This happens for two reasons: particles gain kinetic energy, so they move faster and collide more frequently; more importantly, a much greater proportion of particles have energy equal to or greater than the activation energy, so a much higher fraction of collisions are successful.

升高温度会显著加快反应速率。原因有二：粒子获得动能，运动更快，碰撞更频繁；更重要的是，具有等于或大于活化能能量的粒子比例大大增加，因此有效碰撞的比例大大提高。

A small temperature rise can produce a large increase in rate. In many reactions near room temperature, a 10 °C rise roughly doubles the rate.

温度稍微升高，速率便会大幅增加。许多在室温附近的反应，温度每升高 10 °C，速率约增加一倍。

The energy distribution of particles can be shown by a Maxwell–Boltzmann distribution. As temperature increases, the curve shifts to the right and flattens, showing more particles possess high energies above the activation energy threshold.

粒子的能量分布可用麦克斯韦-玻尔兹曼分布表示。温度升高时，曲线右移且变得扁平，表明更多粒子具有超过活化能的高能量。

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6. Factors Affecting Rate: Surface Area | 影响速率的因素：表面积

For solid reactants, breaking the solid into smaller pieces increases its surface area. This exposes more solid particles at the surface to collisions with particles in solution or gas, increasing the frequency of successful collisions per unit time.

对于固体反应物，将固体研碎成小块可增大其表面积。这使得更多固体粒子暴露在表面，能与溶液或气体中的粒子发生碰撞，提高单位时间内的有效碰撞频率。

A powder reacts faster than large lumps of the same solid. In a reaction like marble chips (calcium carbonate) with hydrochloric acid, powdered marble produces carbon dioxide much more rapidly than large chips.

粉末比同质量的大块固体反应快。在大理石碎片（碳酸钙）与盐酸的反应中，大理石粉末产生二氧化碳的速率远快于大块碎片。

Catalysts in the form of fine powders or porous structures also provide a very high surface area to speed up reactions.

以细粉或多孔结构形式存在的催化剂也能提供极大的表面积来加速反应。

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7. Factors Affecting Rate: Catalysts | 影响速率的因素：催化剂

A catalyst is a substance that increases the rate of a chemical reaction without itself being chemically changed or used up at the end of the reaction. It works by providing an alternative reaction pathway with a lower activation energy.

催化剂是一种能增大化学反应速率，而本身在反应结束时化学性质和质量均不发生变化的物质。它通过提供一条活化能更低的替代反应途径而起作用。

Because the activation energy is lowered, a greater proportion of particles have sufficient energy to react at a given temperature, so the frequency of successful collisions increases.

由于活化能降低，在给定温度下有足够能量发生反应的粒子比例增加，因此有效碰撞频率增大。

Catalysts are specific to particular reactions. Enzymes are biological catalysts that speed up reactions in living organisms. In industrial processes, catalysts such as iron (Haber process) or vanadium(V) oxide (Contact process) are used to increase efficiency.

催化剂对特定反应有专一性。酶是生物催化剂，能加速生物体内的反应。在工业过程中，使用铁（哈伯法）或五氧化二钒（接触法）等催化剂来提高效率。

When drawing an energy profile diagram, a catalyst lowers the activation energy peak without changing the enthalpy change (ΔH) of the reaction.

在绘制能量变化图时，催化剂会降低活化能峰值，但不改变反应的热焓变化 (ΔH)。

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8. Energy Profile Diagrams and Activation Energy | 能量变化图与活化能

An energy profile diagram shows the energy of reactants, products, and the activation energy barrier for a reaction. For an exothermic reaction, the products have lower energy than the reactants; for an endothermic reaction, the products have higher energy.

能量变化图显示反应物、产物的能量以及反应的活化能势垒。放热反应中，产物能量低于反应物；吸热反应中，产物能量高于反应物。

The peak of the curve represents the transition state (activated complex). The difference in energy between reactants and the peak is the activation energy, Eₐ. The overall energy change, ΔH, is the difference between reactants and products.

曲线最高点代表过渡态（活化络合物）。反应物与峰值之间的能量差即为活化能 Eₐ。整体能量变化 ΔH 是反应物和产物之间的能量差。

With a catalyst, a new curve is drawn with a lower peak, showing a reduced Eₐ. The ΔH remains unchanged.

有催化剂时，需画一条峰值较低的新曲线，表示 Eₐ 降低。ΔH 保持不变。

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9. Interpreting Rate Graphs | 解读速率图

Graphs of quantity of product (or amount of reactant) against time allow us to compare reaction rates under different conditions. A steeper slope means a faster rate.

绘制产物量（或反应物量）随时间变化的图，可以比较不同条件下的反应速率。斜率越陡，速率越快。

• For a reaction that goes to completion, the curve becomes horizontal when the limiting reactant is used up.
• 对于进行到完成的反应，当限制反应物耗尽时曲线会变得水平。
• If you compare two graphs: the curve that rises more steeply at the beginning has a higher initial rate. The final amount of product is usually the same if the same amounts of reactants are used (except when a catalyst enables a different reaction pathway).
• 比较两条曲线：开始时上升更陡的那条具有更高的初始速率。如果使用相同量的反应物，最终的产物量通常相同（除非催化剂开启了不同的反应路径）。
• To find the rate at a specific time, draw a tangent to the curve at that point and calculate its gradient: Rate = Change in y / Change in x.
• 求某一时刻的速率，需在该点画切线并计算斜率：速率 = y 的变化量 / x 的变化量。

For experiments investigating the disappearing cross, a graph of 1/time is often plotted against concentration. A straight line through the origin indicates that rate is directly proportional to concentration.

在探究消失十字的实验中，常以 1/时间 对浓度作图。一条过原点的直线表明速率与浓度成正比。

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10. Practical: Effect of Concentration on Rate (Disappearing Cross Experiment) | 实验：浓度对速率的影响（消失十字实验）

This classic IGCSE experiment uses sodium thiosulfate solution and dilute hydrochloric acid to produce a sulfur precipitate that turns the mixture cloudy. The reaction: Na₂S₂O₃(aq) + 2HCl(aq) → S(s) + SO₂(g) + H₂O(l) + 2NaCl(aq).

这个经典的 IGCSE 实验使用硫代硫酸钠溶液和稀盐酸，生成硫沉淀使混合液变浑浊。反应：Na₂S₂O₃(aq) + 2HCl(aq) → S(s) + SO₂(g) + H₂O(l) + 2NaCl(aq)。

Procedure: A cross is drawn on a piece of paper and a conical flask is placed on it. A known volume of sodium thiosulfate solution of a certain concentration is measured into the flask. A known volume of acid is added, the stopwatch started, and the time taken for the cross to disappear from view is recorded. The experiment is repeated with different concentrations of thiosulfate (keeping total volume constant by adding water).

步骤：在纸上画一个十字，将锥形瓶放在上面。量取一定体积、一定浓度的硫代硫酸钠溶液倒入瓶中。加入一定体积的酸，启动秒表，记录十字从视线中消失的时间。用不同浓度的硫代硫酸钠重复实验（通过加水保持总体积不变）。

Analyzing: Plot a graph of 1/time (proportional to rate) against concentration of sodium thiosulfate. If the graph is a straight line through the origin, the rate is directly proportional to concentration.

分析：以 1/时间（与速率成正比）对硫代硫酸钠浓度作图。若得到过原点的直线，则速率与浓度成正比。

Safety: Sulfur dioxide gas is produced – carry out in a well-ventilated lab or use a fume cupboard. Wear goggles.

安全：产生二氧化硫气体——在通风良好的实验室或通风橱中进行。佩戴护目镜。

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11. Practical: Effect of Surface Area on Rate (Marble Chips and Acid) | 实验：表面积对速率的影响（大理石碎片与酸）

Calcium carbonate (marble) reacts with hydrochloric acid to produce carbon dioxide: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The rate can be followed by measuring the volume of gas produced using a gas syringe, or by monitoring mass loss.

碳酸钙（大理石）与盐酸反应生成二氧化碳：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。可通过气体注射器测量气体体积，或通过质量减少来跟踪反应速率。

To investigate surface area, keep the mass of marble and the concentration and volume of acid constant. Use either large chips or small chips/powder of the same total mass. The powdered marble reacts faster, giving a steeper slope on the volume–time graph; the final volume of CO₂ is the same because the same mass of CaCO₃ is used.

探究表面积时，保持大理石质量、酸的浓度和体积不变。使用总质量相同的大块碎片或小碎片/粉末。粉末大理石反应更快，在体积-时间图上斜率更陡；最终 CO₂ 体积相同，因为使用的 CaCO₃ 质量相同。

This experiment also demonstrates that the final amount of product is independent of rate.

该实验还证明最终产物量与速率无关。

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12. Summary and Exam Tips | 总结与应试技巧

Factor | 因素	Effect on Rate | 对速率的影响	Collision Theory Explanation | 碰撞理论解释
Concentration / Pressure | 浓度 / 压强	Rate increases | 速率增大	More particles per unit volume → more frequent collisions | 单位体积粒子数增多 → 碰撞更频繁
Temperature | 温度	Rate increases significantly | 速率显著增大	Particles move faster AND more particles have energy ≥ Eₐ → more frequent successful collisions | 粒子运动加快；而且更多粒子能量 ≥ Eₐ → 有效碰撞更频繁
Surface Area | 表面积	Rate increases | 速率增大	More solid particles exposed → more frequent collisions | 暴露固体粒子增多 → 碰撞更频繁
Catalyst | 催化剂	Rate increases | 速率增大	Provides alternative pathway with lower Eₐ → greater proportion of particles have enough energy to react | 提供 Eₐ 更低的替代路径 → 有足够能量反应的粒子比例更大

Exam Keywords: When explaining rate changes, always mention ‘frequency of successful collisions’ and, for temperature and catalysts, refer to the activation energy and the proportion of particles with energy ≥ Eₐ.

应试关键词：解释速率变化时，务必提到“有效碰撞的频率”；对于温度和催化剂，还要提到活化能以及能量 ≥ Eₐ 的粒子比例。

Be precise with units: concentration changes in mol dm⁻³, gas volumes in cm³, times in s or min. Use correct formulas for rate calculations and be ready to draw tangents on graphs.

单位使用要准确：浓度变化用 mol dm⁻³，气体体积用 cm³，时间用 s 或 min。使用正确的速率计算公式，并准备好再图上画切线。

Common pitfalls: confusing the effect of surface area with concentration, forgetting that mass loss methods require a balance reading that decreases, and not accounting for the constant total volume in dilution experiments.

常见错误：混淆表面积和浓度的影响，忘记质量减少法需要读取递减的天平示数，以及稀释实验中未保持总体积不变。

Practice drawing and interpreting energy profile diagrams with and without catalysts. Remember that a catalyst does not change the amount of product, only the rate.

练习绘制并解读有催化剂和无催化剂的能量变化图。记住催化剂不改变产物量，只改变速率。

Published by TutorHao | Chemistry Revision Series | aleveler.com

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