📚 Rates of Reaction: Factors and Measurement | 反应速率：影响因素与测量
Rates of reaction is one of the most important topics in IGCSE Science (Edexcel). It explains how fast chemical reactions occur and why some reactions are instantaneous while others take years. Understanding this topic requires mastery of collision theory, the five factors that affect reaction rate, and the graphical methods used to measure speed.
反应速率是 IGCSE 科学（Edexcel）中最重要的话题之一。它解释了化学反应发生的快慢，以及为什么有些反应瞬间完成，而另一些则需要数年。掌握这一话题需要深入理解碰撞理论、影响反应速率的五大因素，以及用于测量快慢的图表方法。
1. What Is Rate of Reaction? | 什么是反应速率？
The rate of a chemical reaction is a measure of how quickly reactants are converted into products. It can be expressed as the change in the amount of a reactant or product per unit time.
化学反应速率是衡量反应物转化为产物快慢的物理量。它可以用单位时间内反应物或产物量的变化来表示。
Rate = Change in amount of reactant or product ÷ Time taken
反应速率 = 反应物或产物量的变化 ÷ 所用时间
erage rate is 0.5 ÷ 25 = 0.02 g/s. This tells us how fast the magnesium is being consumed.
例如，若 0.5 g 镁在 25 秒内与盐酸完全反应，则平均速率为 0.5 ÷ 25 = 0.02 g/s。这告诉我们镁被消耗的速率。
Units for rate are usually g/s, cm³/s, mol/s, or g/min depending on what is being measured. In IGCSE exams, you must always state the unit in your final answer.
速率的单位通常是 g/s、cm³/s、mol/s 或 g/min，具体取决于测量的对象。在 IGCSE 考试中，最终答案必须注明单位。
2. Measuring Reaction Rates | 测量反应速率
There are several practical methods to measure how fast a reaction proceeds. The choice of method depends on whether a gas, a solid, or a colour change is involved.
有若干实验方法可用来测量反应进行的快慢。选择哪种方法取决于反应中涉及气体、固体还是颜色变化。
Gas collection (measuring gas volume): Use a gas syringe or an inverted burette over water. Record the volume of gas produced every 10 or 20 seconds.
气体收集（测量气体体积）： 使用气体注射器或倒置于水中的滴定管。每 10 或 20 秒记录一次产生的气体体积。
Loss of mass: Place the reaction flask on a balance. As gas escapes, the mass decreases. Record mass at regular intervals.
质量损失法： 将反应烧瓶放在天平上。随着气体逸出，质量减小。每隔一定时间记录质量。
Disappearance of a cross: Place a flask on a white tile with a black cross underneath. Time how long it takes for the cross to disappear as a precipitate forms.
十字消失法： 将烧瓶放在白瓷砖上，下方放置黑色十字。记录沉淀生成使十字消失所需的时间。
Change in pH or colour: Use a pH meter or colorimeter to track the progress of reactions that involve acids or coloured species.
pH 或颜色变化： 使用 pH 计或比色计追踪涉及酸或有色物质的反应进程。
In the Edexcel practical exam, you may be asked to choose a suitable method and explain why it is appropriate. For reactions producing a gas, gas collection is preferred; for reactions with a visible colour change, the cross method is simpler.
在 Edexcel 实验考试中，你可能会被要求选择合适的方法并解释原因。对于产生气体的反应，首选气体收集法；对于有明显颜色变化的反应，十字法更简单。
3. Collision Theory | 碰撞理论
Collision theory states that for a reaction to occur, reactant particles must collide with each other with sufficient energy (greater than or equal to the activation energy) and the correct orientation.
碰撞理论指出，要使反应发生，反应物颗粒必须相互碰撞，且碰撞能量充足（大于或等于活化能）并具有正确的取向。
Successful collision = correct orientation + energy ≥ activation energy (Eₐ)
有效碰撞 = 正确取向 + 能量 ≥ 活化能（Eₐ）
Not every collision leads to a reaction. A collision that does result in a reaction is called a successful or effective collision. Increasing the frequency of successful collisions increases the rate of reaction.
并非每次碰撞都能引发反应。能导致反应的碰撞称为有效碰撞。提高有效碰撞的频率即可加快反应速率。
The activation energy is the minimum energy that colliding particles need in order to break existing bonds and start the reaction. Catalysts work by lowering this activation energy.
活化能是碰撞颗粒为破坏现有化学键并启动反应所需的最低能量。催化剂通过降低活化能来发挥作用。
In exams, a common mistake is to say "more collisions" without mentioning "successful collisions" or "with sufficient energy". Always be precise.
考试中常见的错误是只说"更多碰撞"，而不提"有效碰撞"或"具有足够能量"。用词务必精确。
4. Surface Area | 表面积
Increasing the surface area of a solid reactant increases the rate of reaction. This is because more particles are exposed and therefore available for collisions with other reactant particles.
增大固体反应物的表面积会加快反应速率。这是因为更多颗粒暴露在外，从而更易与其他反应物颗粒发生碰撞。
Consider marble chips (calcium carbonate) reacting with hydrochloric acid. Powdered calcium carbonate reacts much faster than large lumps because the powder has a much larger total surface area.
以大理石碎片（碳酸钙）与盐酸的反应为例。粉末状碳酸钙的反应速率远大于大块固体，因为粉末的总表面积大得多。
If you double the number of exposed particles, you approximately double the frequency of collisions, and therefore the rate increases roughly proportionally (at constant temperature and concentration).
若暴露的颗粒数量翻倍，碰撞频率大约翻倍，因此在温度和浓度不变的情况下，速率大致成比例增加。
Graphically, a powder gives a steeper curve that levels off sooner, but the final amount of product is identical because the same mass of reactant is used.
从图形上看，粉末给出的曲线更陡峭且更早趋于平缓，但由于使用了相同质量的反应物，最终产物总量相同。
5. Concentration and Pressure | 浓度与压强
Increasing the concentration of a solution increases the rate of reaction. A higher concentration means more solute particles in the same volume, so collisions between reactant particles become more frequent.
增大溶液浓度会加快反应速率。浓度越高，同一体积内溶质颗粒越多，反应物颗粒间的碰撞就越频繁。
For gases, increasing the pressure has the same effect as increasing concentration: gas particles are squeezed into a smaller volume, so they collide more often.
对于气体，增大压强与增大浓度效果相同：气体颗粒被压缩到更小体积中，碰撞更加频繁。
Note that concentration and pressure do not change the activation energy. They only change the number of collisions per second. The proportion of successful collisions remains roughly the same.
请注意，浓度和压强不会改变活化能。它们只改变每秒的碰撞次数。有效碰撞的比例大致保持不变。
In a concentration experiment, use the same volume of acid but different concentrations (e.g., 0.5 mol/dm³, 1.0 mol/dm³, 2.0 mol/dm³). Keep temperature, mass of solid, and surface area constant to ensure a fair test.
在浓度实验中，使用相同体积但不同浓度的酸（例如 0.5 mol/dm³、1.0 mol/dm³、2.0 mol/dm³）。保持温度、固体质量和表面积不变，以确保公平对照。
6. Temperature | 温度
Raising the temperature increases the rate of reaction significantly. According to the kinetic theory, particles gain kinetic energy and move faster, so collisions occur more frequently.
升高温度会显著加快反应速率。根据动力学理论，颗粒获得动能并运动加快，因而碰撞更加频繁。
More importantly, a higher temperature increases the proportion of particles that have energy equal to or greater than the activation energy. This means a much larger fraction of collisions are successful.
更重要的是，温度升高增加了能量达到或超过活化能的颗粒比例。这意味着有效碰撞所占比例大大增加。
As a rough rule of thumb for IGCSE, a 10°C rise in temperature roughly doubles the rate of reaction. This is why food spoils faster in warm weather and why refrigerators slow down chemical reactions.
作为 IGCSE 的粗略经验法则，温度每升高 10°C，反应速率大约翻倍。这就是为什么食物在温暖天气中变质更快，而冰箱能减缓化学反应。
On a graph, higher temperature gives a steeper initial slope and the reaction finishes sooner. The maximum product amount remains the same, as long as the limiting reactant is unchanged.
在图表上，更高的温度产生更陡的初始斜率，反应更早结束。只要限制反应物不变，最大产物量保持不变。
7. Catalysts | 催化剂
A catalyst is a substance that speeds up a reaction without being used up itself. It provides an alternative reaction pathway with a lower activation energy.
催化剂是一种能加快反应而自身不被消耗的物质。它为反应提供了一条活化能较低的新路径。
Catalyst lowers Eₐ → more particles have sufficient energy → faster rate
催化剂降低 Eₐ → 更多颗粒拥有足够能量 → 反应加快
Common examples in IGCSE include: manganese(IV) oxide (MnO₂) for decomposing hydrogen peroxide, iron in the Haber process, and enzymes as biological catalysts in digestion.
IGCSE 中的常见例子包括：二氧化锰（MnO₂）催化过氧化氢分解、哈伯法中的铁催化剂，以及作为消化中生物催化剂的酶。
Catalysts do not change the position of equilibrium or the final amount of product; they only help the system reach equilibrium faster. They are also specific — different reactions need different catalysts.
催化剂不会改变平衡位置或最终产物量，它们只是帮助系统更快达到平衡。催化剂还具有专一性——不同反应需要不同的催化剂。
Enzymes are special biological catalysts that work best at an optimum temperature (usually around 37°C in humans) and an optimum pH. If the temperature gets too high, enzymes denature and stop working.
酶是特殊的生物催化剂，在最佳温度（人体内通常为 37°C 左右）和最佳 pH 下活性最高。温度过高时，酶会变性失活。
8. Graphical Analysis | 图表分析
Reaction progress is often shown on a graph of product volume (or mass loss) against time. The steeper the curve, the faster the reaction.
反应进程通常以产物体积（或质量损失）对时间作图来表示。曲线越陡，反应越快。
Three key features to analyse:
需要分析三个关键特征：
Initial slope (gradient): The steeper the initial slope, the faster the initial rate.
初始斜率： 初始斜率越陡，初始速率越快。
Levelling off: When the line becomes horizontal, the reaction has stopped because at least one reactant is used up.
趋于平缓： 当曲线变为水平时，反应停止，因为至少一种反应物已耗尽。
Height of the plateau: The final volume of gas tells you the total amount of product, which depends only on the quantity of limiting reactant.
平台高度： 最终气体体积表示产物总量，仅取决于限制反应物的量。
To calculate the average rate from a graph, divide the total change in product by the total time. To find the rate at a specific moment, draw a tangent to the curve at that point and calculate its gradient.
从图表计算平均速率时，将产物总变化量除以总时间。要计算某一时刻的速率，需在该点画切线并求其斜率。
When comparing two curves, remember: if the final plateau is at the same height, the same amount of product was formed; a steeper curve simply means it formed faster.
比较两条曲线时请记住：若最终平台高度相同，则生成的产物量相同；曲线更陡只意味着生成得更快。
9. Comparing Rates of Reaction | 比较反应速率
When comparing reactions, it is useful to calculate the rate in the first few seconds. This is often done by measuring the volume of gas produced in the first 10 or 20 seconds and dividing by the time.
比较反应时，通常计算最初几秒内的速率。常用方法是将前 10 或 20 秒内产生的气体体积除以时间。
Consider the reaction between magnesium and hydrochloric acid:
考虑镁与盐酸的反应：
| Condition 条件 | Gas in first 20 s 前 20 秒气体量 | Initial rate 初始速率 |
| Low concentration 低浓度 | 12 cm³ | 0.6 cm³/s |
| High concentration 高浓度 | 24 cm³ | 1.2 cm³/s |
The table shows that doubling the concentration doubles the initial rate, demonstrating a proportional relationship in this example.
上表显示，浓度加倍使初始速率加倍，在此例中体现了比例关系。
This method of "gas volume in fixed time" is quick and does not require drawing tangents, making it ideal for exam questions and practical write-ups.
"固定时间内的气体体积"方法快速简便，无需画切线，非常适合考试题目和实验报告。
10. Reversible Reactions and Equilibrium | 可逆反应与平衡
Some reactions are reversible. In a closed system, a reversible reaction can reach dynamic equilibrium, where the forward and backward reactions occur at the same rate.
某些反应是可逆的。在封闭体系中，可逆反应可以达到动态平衡，此时正反应和逆反应速率相等。
At equilibrium, the concentrations of reactants and products remain constant. This does not mean the reactions have stopped — they are still happening, but at equal rates.
在平衡状态下，反应物和产物的浓度保持不变。这并不意味着反应停止——反应仍在进行，只是速率相等。
For the Edexcel IGCSE, you need to know that changing temperature, pressure, or concentration can shift the position of equilibrium. A catalyst speeds up the attainment of equilibrium but does not shift its position.
对于 Edexcel IGCSE，你需要知道改变温度、压强或浓度会移动平衡位置。催化剂能加速达到平衡，但不会移动平衡位置。
An example is the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + heat. The forward reaction is exothermic, so lower temperatures favour ammonia production — but too low a temperature makes the rate impractically slow.
以哈伯法为例：N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + 热量。正反应放热，因此较低温度有利于氨的生成——但温度过低会使速率慢到不切实际。
11. Industrial Applications | 工业应用
Controlling reaction rates is vital in industry. Manufacturers need reactions to be fast enough to be economical, but not so fast that they become dangerous or uncontrollable.
在工业中，控制反应速率至关重要。生产商需要反应足够快以保证经济效益，但又不能快到危险或失控。
The Haber process for ammonia uses an iron catalyst, a temperature of about 450°C, and a pressure of 200 atmospheres. These conditions balance rate, yield, and cost.
哈伯法制氨使用铁催化剂，温度约为 450°C，压强约为 200 个大气压。这些条件平衡了速率、产率和成本。
In food preservation, lower temperatures slow down the chemical reactions that cause spoilage. This is why milk is refrigerated and food is frozen.
在食品保藏中，较低温度能减缓导致变质的化学反应。这就是牛奶需要冷藏、食物需要冷冻的原因。
Catalytic converters in cars speed up the conversion of toxic gases like carbon monoxide and nitrogen oxides into less harmful substances. They use platinum and rhodium as catalysts.
汽车中的催化转化器可加速将一氧化碳和氮氧化物等有毒气体转化为危害较小的物质。它使用铂和铑作为催化剂。
Understanding reaction rates also matters in medicine: aspirin and other drugs are designed to dissolve at controlled rates in the body, ensuring effective and safe release.
理解反应速率在医学中同样重要：阿司匹林等药物被设计为在体内以可控速率溶解，确保有效且安全地释放。
12. Common Exam Mistakes and How to Avoid Them | 常见考试错误及规避方法
Students often lose marks on this topic due to imprecise language. Below are the most frequent errors and the correct way to phrase answers.
学生常因语言不精确而在这一话题上失分。以下是最高频的错误及正确的作答方式。
Mistake: "The particles collide more." Fix: "The frequency of successful collisions increases because more particles have energy ≥ Eₐ."
错误： "颗粒碰撞更多。" 纠正： "有效碰撞频率增加，因为有更多颗粒的能量 ≥ Eₐ。"
Mistake: "A catalyst makes the reaction faster because it gives particles energy." Fix: "A catalyst provides an alternative pathway with lower activation energy."
错误： "催化剂使反应加快是因为它给了颗粒能量。" 纠正： "催化剂提供了活化能更低的新路径。"
Mistake: "Temperature increases the rate because particles collide harder." Fix: " particles collide more frequently and a greater proportion of collisions have energy ≥ Eₐ."
错误： "温度升高使速率加快是因为颗粒撞得更猛。" 纠正： "温度升高使动能增加，因此碰撞更频繁，且更大比例的碰撞能量 ≥ Eₐ。"
Mistake: Forgetting to state units in rate calculations. Fix: Always include units such as cm³/s or g/s in every rate answer.
错误： 在速率计算中忘记写单位。 纠正： 每个速率答案都要包含 cm³/s 或 g/s 等单位。
Mistake: Confusing rate with yield. Fix: Rate is how fast a reaction proceeds; yield is how much product is formed. A catalyst affects rate, not yield.
错误： 混淆速率与产率。 纠正： 速率是反应进行的快慢；产率是生成的产物量。催化剂影响速率，不影响产率。
Another common error involves temperature in exothermic reactions. Even if the forward reaction is exothermic, raising the temperature always speeds up both the forward and reverse reactions — but it increases the reverse rate more, shifting equilibrium in the endothermic direction.
另一个常见错误涉及放热反应中的温度。即使正向反应放热，升高温度也总会同时加快正逆反应——但逆反应速率增加得更多，从而使平衡向吸热方向移动。
Finally, always check whether the question asks about initial rate, average rate, or rate at a specific time. Each requires a different approach in calculation.
最后，务必看清题目问的是初始速率、平均速率还是某一时刻的速率。三者的计算方法各不相同。
13. Practice Questions | 练习题
Try these questions to test your understanding before the exam.
考试前请尝试以下问题来检验你的理解。
Question 1: A student adds 0.10 g of magnesium powder to 50 cm³ of 1.0 mol/dm³ hydrochloric acid at 25°C. The reaction produces 80 cm³ of hydrogen gas in 40 seconds. Calculate the average rate of gas production in cm³/s.
问题 1： 学生在 25°C 下将 0.10 g 镁粉加入 50 cm³ 的 1.0 mol/dm³ 盐酸中。反应在 40 秒内产生 80 cm³ 氢气。计算平均产气速率（cm³/s）。
Answer: Rate = 80 ÷ 40 = 2.0 cm³/s
答案：速率 = 80 ÷ 40 = 2.0 cm³/s
Question 2: Explain, in terms of particles, why increasing the concentration of hydrochloric acid from 1.0 mol/dm³ to 2.0 mol/dm³ increases the rate of reaction with magnesium.
问题 2： 从粒子角度解释，为什么将盐酸浓度从 1.0 mol/dm³ 增至 2.0 mol/dm³ 会加快与镁的反应速率。
Model answer: In a higher concentration, there are more acid particles per unit volume. This increases the frequency of successful collisions between acid particles and magnesium atoms, so the rate of reaction increases.
参考答案： 在较高浓度下，单位体积内酸粒子更多。这增加了酸粒子与镁原子之间的有效碰撞频率，因此反应速率加快。
Question 3: Sketch two curves on the same axes for equal masses of marble chips and marble powder reacting with excess acid. Label each curve and explain the difference in shape.
问题 3： 在同一坐标系中画出等质量大理石碎片和大理石粉末与过量酸反应的两条曲线。标注每条曲线并解释形状差异。
Key points: frequent collisions) but both curves reach the same final height (same mass of reactant).
要点： 粉末曲线初始更陡（表面积更大 → 碰撞更频繁），但两条曲线最终高度相同（反应物质量相同）。
14. Summary of Key Facts | 关键知识总结
Use this quick checklist to revise the essential points before your exam.
考试前请使用这份快速清单来复习要点。
| Factor 因素 | Effect on rate 对速率的影响 | Explanation 解释 |
| Surface area ↑ 表面积增大 | Rate ↑ 速率加快 | More particles exposed → more frequent collisions 暴露粒子更多 → 碰撞更频繁 |
| Concentration ↑ 浓度增大 | Rate ↑ 速率加快 | More particles per volume → more frequent collisions 单位体积粒子更多 → 碰撞更频繁 |
| Pressure ↑ 压强增大 | Rate ↑ 速率加快 | Gas particles compressed → more frequent collisions 气体粒子被压缩 → 碰撞更频繁 |
| Temperature ↑ 温度升高 | Rate ↑ (roughly doubles per 10°C) 速率加快（每 10°C 约翻倍） | More energy → more particles exceed Eₐ 能量更大 → 更多粒子超过 Eₐ |
| Catalyst added 添加催化剂 | Rate ↑ 速率加快 | Lowers activation energy → more successful collisions 降低活化能 → 更多有效碰撞 |
Remember that the final amount of product is determined by the quantity of limiting reactant, not by rate. Changing rate only changes how quickly that final amount is reached.
请记住，最终产物量由限制反应物的量决定，而不由速率决定。改变速率只会改变达到最终产物量的快慢。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图