📚 Understanding Rates of Reaction | 理解反应速率
In chemistry, the rate of reaction measures how quickly reactants are used up or products are formed. This topic is essential for Edexcel IGCSE Science and brings together ideas about particles, energy, and practical methods.
在化学中，反应速率衡量反应物被消耗或产物生成的速度。这一主题对于爱德思 IGCSE 科学考试至关重要，并将粒子、能量与实验方法等概念联系在一起。
1. What is Rate of Reaction? | 什么是反应速率？
The rate of a reaction is the change in the amount of a reactant or product per unit of time. It can be expressed as a change in mass, volume, or concentration over a given time interval.
反应速率是指单位时间内反应物或产物数量的变化。它可以用一定时间内质量、体积或浓度的变化来表示。
Common units include grams per second (g/s), cubic centimetres per second (cm³/s), and moles per second (mol/s). The symbol Δ is used to mean ‘change in’.
常用单位包括克每秒（g/s）、立方厘米每秒（cm³/s）和摩尔每秒（mol/s）。符号 Δ 表示“变化量”。
rate = Δamount / Δtime
2. Measuring Rates | 测定反应速率
There are several practical techniques to measure the rate of a reaction. The choice of method depends on whether a gas is produced, whether the mixture changes colour, or whether mass changes.
测定反应速率有多种实验方法。选择哪种方法取决于反应是否产生气体、混合物是否变色或质量是否发生变化。
If the reaction produces a gas, a gas syringe can collect the volume of gas at regular time intervals. Alternatively, an electronic balance can measure the loss of mass as the gas escapes.
如果反应产生气体，可以使用气体注射器按固定时间间隔收集气体体积。或者，可以使用电子天平测量因气体逸出导致的质量损失。
For reactions that produce a precipitate, the time taken for a cross drawn on paper to disappear from view can be used to estimate the rate.
对于生成沉淀的反应，可以记录纸上画好的十字被遮盖消失所需的时间，从而估计反应速率。
3. Collision Theory | 碰撞理论
The collision theory states that for a reaction to occur, particles must collide with each other in the correct orientation and with enough energy to break existing bonds.
碰撞理论指出，反应若要发生，粒子必须以正确的方向碰撞，并且具有足够的能量来断裂原有的化学键。
The minimum energy that particles need to react is called the activation energy, Eₐ. A successful collision is one that leads to the formation of products.
粒子发生反应所需的最低能量称为活化能，记作 Eₐ。能够生成产物的碰撞称为有效碰撞。
Increasing the number of successful collisions per second increases the rate of reaction.
每秒内有效碰撞次数越多，反应速率就越快。
4. Effect of Temperature | 温度的影响
Raising the temperature increases the kinetic energy of the particles. As a result, particles move faster and collide more frequently.
升高温度会增加粒子的动能。因此，粒子运动更快，碰撞更加频繁。
More importantly, a greater proportion of particles have energy equal to or greater than the activation energy, so a higher fraction of collisions are successful.
更重要的是，具有≥活化能的粒子比例增大，因此碰撞中有效碰撞的比例更高。
In general, an increase of about 10 °C roughly doubles the rate of many reactions.
通常情况下，温度每升高约 10 °C，许多反应的反应速率大约会翻倍。
5. Effect of Concentration and Pressure | 浓度与压力的影响
Increasing the concentration of a dissolved reactant means there are more particles in the same volume. This leads to more frequent collisions between reactant particles.
增加溶液中反应物的浓度，意味着相同体积内有更多粒子，这会导致反应物粒子之间碰撞更加频繁。
For gases, increasing the pressure pushes the particles closer together, which also increases the frequency of collisions.
对于气体，增大压力会使粒子更加靠近，从而同样增加碰撞频率。
Therefore, higher concentration and higher pressure both increase the rate of reaction, provided that the reacting particles are in a state where they can move.
因此，更高的浓度和更高的压力都能提高反应速率，前提是反应粒子处于可自由运动的状态。
6. Effect of Surface Area | 表面积的影响
If a solid reactant is broken into smaller pieces, its total surface area increases. This means that more particles of the solid are exposed to the other reactant.
如果将固体反应物粉碎成更小的颗粒，其总表面积会增大，这意味着固体与另一反应物接触的粒子更多。
With a larger surface area, the number of collisions per second increases, so the reaction rate increases.
表面积越大，每秒内的碰撞次数越多，反应速率也就越高。
A powdered solid reacts faster than a single large lump of the same mass because the powder has a much larger total surface area.
在相同质量下，粉末状固体比一整块大固体反应得快，因为粉末的总表面积大得多。
7. Effect of Catalysts | 催化剂的影响
A catalyst is a substance that speeds up a reaction without being used up in the reaction. It provides an alternative reaction pathway with a lower activation energy.
催化剂是一种能加快反应速率，但自身在反应中不被消耗的物质。它提供了一条活化能更低的替代反应路径。
Because the activation energy is lower, a much larger proportion of particles have enough energy to react successfully at the same temperature.
由于活化能降低，在相同温度下，有更大比例的粒子具有足够的能量进行有效反应。
Catalysts are used in many industrial processes, such as the iron catalyst in the Haber process for making ammonia.
催化剂广泛应用于许多工业过程，例如哈伯法制氨中使用的铁催化剂。
8. Reaction Profiles | 反应能线图
A reaction profile is a graph showing the energy changes during a reaction. The horizontal axis is the progress of the reaction, and the vertical axis is the energy content of the chemicals.
反应能线图是表示反应过程中能量变化的图像。横轴表示反应进程，纵轴表示物质的能量含量。
The activation energy is shown as the height of the energy hill that must be overcome from the reactants to the activated complex.
活化能在图中表现为反应物到活化配合物之间必须跨越的能垒高度。
If the products have lower energy than the reactants, the reaction is exothermic. If the products have higher energy, it is endothermic.
如果产物的能量低于反应物，该反应为放热反应；如果产物的能量高于反应物，则为吸热反应。
9. Graphs and Rate Calculations | 图形与速率计算
Rates of reaction can be studied using graphs of the amount of reactant or product against time. The steeper the line on a graph, the faster the reaction.
反应速率可以通过绘制反应物或产物量与时间的关系图来研究。图中曲线越陡，说明反应越快。
The average rate over a period of time can be calculated using the total change in quantity divided by the total time elapsed.
一段时间内的平均速率可以用总变化量除以经过的总时间来计算。
For a reaction that loses mass, the average rate is calculated as the mass lost divided by the time taken.
对于质量减少的反应，平均速率等于损失的质量除以所用时间。
average rate = total change ÷ total time
10. Industrial Applications | 工业应用
Controlling the rate of reaction is very important in industry. For example, hydrogen peroxide decomposes slowly, but adding manganese dioxide speeds it up safely.
控制反应速率在工业中非常重要。例如，过氧化氢分解较慢，但加入二氧化锰可以安全地加快其分解。
In the Haber process for making ammonia, a higher pressure and a moderate temperature are used together with an iron catalyst to increase the rate while maintaining a good yield.
在哈伯法制氨中，工业上采用高压和适当温度，并加入铁催化剂，以加快反应速率并保持良好的产率。
In food storage, low temperatures are used to slow down the chemical reactions that cause food to spoil.
在食品储存中，利用低温来减慢导致食物腐败的化学反应速率。
11. Summary and Exam Tips | 总结与考试提示
Reaction rate is about how fast reactants become products. The five main factors that affect rate are temperature, concentration, pressure, surface area, and catalysts.
反应速率描述的是反应物转变为产物的快慢。影响速率的主要因素有五个：温度、浓度、压力、表面积和催化剂。
All of these factors work by changing the frequency of collisions or the energy of the colliding particles, based on collision theory.
所有这些因素都是通过改变碰撞频率或碰撞粒子的能量来起作用的，其理论基础是碰撞理论。
When interpreting graphs, always compare the slopes, and remember that a catalyst lowers the activation energy without being used up. Practice drawing reaction profiles and explaining rates in terms of particles.
解读图像时，务必比较曲线斜率；同时记住催化剂能降低活化能且自身不被消耗。多练习绘制反应能线图，并学会从粒子角度解释反应速率。
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