📚 Rates of Reaction | 反应速率
In this revision article, we will explore the concept of reaction rate, the factors that affect it, and how to measure it accurately. Understanding rates of reaction is essential for the Edexcel IGCSE Science examination.
本复习文章将探讨反应速率的概念、影响因素以及如何准确测量它。理解反应速率是 Edexcel IGCSE 科学考试的核心要求。
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 tells us how fast reactants are used up or products are formed.
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。它告诉我们反应物被消耗或产物生成的速度有多快。
rate = change in quantity ÷ time taken
速率 = 量的变化 ÷ 所需时间
Common units for rate are mol/dm³/s (for concentration changes) or cm³/s (for gas volume changes).
速率的常用单位是 mol/dm³/s（用于浓度变化）或 cm³/s（用于气体体积变化）。
2. Measuring Reaction Rates | 测量反应速率
One common method is monitoring the volume of gas produced over time using a gas syringe. Another is measuring the loss of mass when a gas escapes from an open flask.
一种常用的方法是用气体注射器监测一段时间内生成的气体体积。另一种方法是在气体逸出敞口烧瓶时测量质量的减少。
The change in pH or colour can also be followed if the reaction involves acids or coloured species.
如果反应涉及酸或有色物质，也可以跟踪 pH 值或颜色的变化。
A table of results might look like this:
实验结果表格可能如下所示：
| Time (s) | Volume of gas (cm³) | Rate (cm³/s) |
| 0 | 0 | – |
| 10 | 25 | 2.5 |
| 20 | 40 | 1.5 |
3. Collision Theory | 碰撞理论
For a reaction to occur, particles must collide with energy greater than or equal to the activation energy (Eₐ) and with the correct orientation.
要使反应发生，粒子必须发生碰撞，且碰撞能量大于或等于活化能（Eₐ），同时碰撞方向要正确。
Not every collision leads to a reaction; only effective collisions produce a chemical change.
并非每次碰撞都会引发反应；只有有效碰撞才会产生化学变化。
Successful collision = correct orientation + enough energy
成功碰撞 = 正确取向 + 足够能量
4. Concentration and Pressure | 浓度与压强
Increasing the concentration of a reactant increases the number of particles per unit volume. The collision frequency rises, so more effective collisions occur per second and the rate increases.
增加反应物浓度会增加单位体积内的粒子数。碰撞频率升高，每秒发生的有效碰撞增多，速率因此加快。
For gases, increasing pressure has the same effect as increasing concentration because the particles are squeezed into a smaller volume.
对于气体，增大压强与增大浓度效果相同，因为粒子被压缩到更小的体积中。
5. Temperature | 温度
Raising the temperature makes particles move faster and collide more often. More importantly, a greater proportion of particles have energy above Eₐ, so the fraction of successful collisions increases dramatically.
升高温度使粒子运动加快、碰撞更频繁。更重要的是，具有高于 Eₐ 能量的粒子比例增大，因此成功碰撞的比例大幅上升。
A general rule is that a 10°C rise in temperature roughly doubles the rate of many reactions.
一般经验法则是：温度每升高 10°C，许多反应的速率大约翻倍。
6. Surface Area | 表面积
Breaking a solid into smaller pieces increases its surface area to volume ratio. More particles are exposed, so collisions between solid and solution particles become more frequent.
把固体研碎成小块会增大其表面积与体积之比。更多粒子暴露出来，因此固体与溶液粒子之间的碰撞更加频繁。
This explains why powdered calcium carbonate reacts faster with acid than large marble chips.
这解释了为什么粉末状碳酸钙与酸反应比大块大理石块更快。
7. Catalysts | 催化剂
A catalyst is a substance that speeds up a reaction without being used up. It provides an alternative pathway with a lower activation energy.
催化剂是一种能加快反应速率但自身不被消耗的物质。它为反应提供了一条活化能更低的替代路径。
Catalysts are specific to particular reactions and are important in industry because they reduce the energy cost of processes such as the Haber process and catalytic converters.
催化剂具有专一性，在工业中非常重要，因为它们能降低哈伯法、汽车催化转化器等过程的能源成本。
8. Reaction Rate Graphs | 反应速率曲线图
A graph of product volume against time starts steep and becomes flat. The steepest part at the start shows the highest rate; the flat line means the reaction has stopped because a reactant is used up.
产物体积对时间的曲线始于陡峭并逐渐变平。起点处最陡的部分表示速率最高；平坦线段表示反应已停止，因为某种反应物已耗尽。
The average rate can be found from the slope of the straight-line portion, and the instantaneous rate can be found by drawing a tangent to the curve at a given time.
平均速率可由直线部分的斜率求得，瞬时速率则可通过在曲线上某一点作切线得到。
9. Calculating Rates | 计算反应速率
For a reaction producing gas, the rate can be calculated from the volume of gas collected in a fixed interval.
对于产生气体的反应，速率可以根据固定时间间隔内收集的气体体积计算。
average rate = total gas volume ÷ total time
平均速率 = 气体总体积 ÷ 总时间
For reactions such as Mg + 2HCl → MgCl₂ + H₂, the mass loss method is useful because hydrogen gas escapes from the flask.
对于 Mg + 2HCl → MgCl₂ + H₂ 这类反应，质量损失法很适用，因为氢气会从烧瓶中逸出。
10. Industrial Applications | 工业应用
Industries use high pressure, high temperature and catalysts to make reactions faster and more economical. For example, the Haber process uses iron as a catalyst at 450°C and 200 atm.
工业上通过高压、高温和催化剂来加快反应并提高经济效益。例如，哈伯法使用铁作催化剂，条件为 450°C 和 200 atm。
However, a balance is needed: higher temperatures increase rate but reduce the yield of exothermic reactions, so the conditions are chosen to optimise both factors.
然而，需要平衡：升高温度会加快速率，但会降低放热反应的产率，因此要选择能兼顾两者的条件。
11. Summary | 总结
The rate of reaction is controlled by collision theory. Increasing concentration, pressure, temperature, surface area or adding a catalyst all increase the rate.
反应速率由碰撞理论控制。增大浓度、压强、温度、表面积或加入催化剂都会加快反应。
You should be able to interpret rate graphs, calculate rates from data, and explain each factor in terms of collisions and activation energy.
你应该能够解读速率曲线、根据数据计算速率，并从碰撞和活化能的角度解释各个因素。
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