📚 Rate of Reaction | 化学反应速率
This revision guide covers the key concepts of reaction rate for the Edexcel IGCSE Science (Double Award) syllabus. You will learn what reaction rate means, how it is measured, and which factors change it. Each idea is explained in English with a matching Chinese translation.
本复习指南涵盖 Edexcel IGCSE 科学（双奖）大纲中反应速率的核心概念。你将学习反应速率的含义、如何测量它，以及哪些因素会改变它。每个概念均以英文解释，并配有对应的中文翻译。
1. What is Reaction Rate? | 什么是反应速率
Reaction rate describes how quickly the amount of a reactant decreases or the amount of a product increases during a chemical reaction. It is often expressed as a change in concentration per unit time.
反应速率描述化学反应中反应物量减少或产物量增加的快慢。它通常表示为单位时间内浓度的变化。
Rate = Δ(Reactant) ⁄ Δt = Δ(Product) ⁄ Δt
Here Δ means "change in" and t is time. A faster reaction has a larger rate value.
这里 Δ 表示“变化量”，t 是时间。反应越快，速率值越大。
2. Measuring Reaction Rate | 测量反应速率
Several practical methods are used to follow a reaction. The choice depends on whether a reactant or product is a gas, a coloured solution, or a solid.
实际中常用多种方法追踪反应。选择哪种方法取决于反应物或产物是气体、有色溶液还是固体。
Measure the volume of gas produced with a gas syringe.
使用气体注射器测量产生的气体体积。
Measure the mass lost from the flask when a gas escapes.
当气体逸出时测量锥形瓶的质量损失。
Use a colorimeter to monitor colour intensity changes.
使用色度计监测颜色强度的变化。
Use a timer and observe precipitation (cloudiness) with a cross mark.
用计时器观察沉淀（浑浊）造成十字标记变模糊。
3. Collision Theory | 碰撞理论
For a reaction to happen, particles must collide with each other. They also need sufficient energy (equal to or greater than the activation energy) and the correct orientation.
化学反应发生需要粒子相互碰撞。它们还必须具有足够的能量（等于或大于活化能），并且碰撞方向正确。
The activation energy is the minimum energy needed for a collision to lead to a reaction. Only a small fraction of collisions are successful.
活化能是碰撞引发反应所需的最小能量。只有一小部分碰撞是有效的。
Any change that increases the frequency of successful collisions will increase the reaction rate.
任何能增加有效碰撞频率的变化都会提高反应速率。
4. Factor: Concentration | 影响因素：浓度
Increasing the concentration of a dissolved reactant means more particles are present in the same volume. This leads to more frequent collisions between reactant particles.
增加溶解反应物的浓度意味着同一体积内有更多粒子。这导致反应物粒子之间的碰撞更频繁。
As collision frequency increases, the number of successful collisions per second also increases, so the rate becomes faster.
由于碰撞频率增加，每秒有效碰撞的次数也增加，因此反应速率变快。
5. Factor: Pressure | 影响因素：压力
For reactions involving gases, increasing pressure compresses the gas into a smaller volume. The number of gas particles per unit volume increases.
对于涉及气体的反应，增大压力将气体压缩到更小体积。单位体积内的气体粒子数增加。
This results in more frequent collisions between gas molecules, so the reaction rate rises.
这导致气体分子之间碰撞更频繁，因此反应速率升高。
6. Factor: Temperature | 影响因素：温度
Higher temperature gives particles more kinetic energy. They move faster, so collisions occur more often.
较高温度赋予粒子更多动能。它们运动更快，因此碰撞发生的频率更高。
More importantly, a greater proportion of particles now have energy equal to or greater than the activation energy. This greatly increases the number of successful collisions.
更重要的是，现在更大比例的粒子具有等于或大于活化能的能量。这大大增加了有效碰撞的次数。
7. Factor: Surface Area | 影响因素：表面积
For solid reactants, only particles on the surface can collide with other particles. Breaking a solid into smaller pieces increases its total surface area.
对于固体反应物，只有表面上的粒子才能与其他粒子碰撞。将固体碎成更小的颗粒会增大其总表面积。
A larger surface area exposes more particles to collisions, so the frequency of successful collisions increases and the reaction is faster.
更大的表面积为更多粒子提供暴露面，因此有效碰撞频率增加，反应更快。
8. Factor: Catalyst | 影响因素：催化剂
A catalyst is a substance that increases the rate of reaction without being used up. It works by providing an alternative reaction pathway with a lower activation energy.
催化剂是能提高反应速率而不被消耗的物质。它通过提供一条活化能较低的替代反应途径来起作用。
With a lower activation energy, more particles have enough energy to react at a given temperature, so successful collisions become more frequent.
由于活化能较低，在给定温度下更多粒子具有足够能量发生反应，因此有效碰撞更加频繁。
Catalysts are important in industry because they save energy and time.
催化剂在工业中非常重要，因为它们节省能源和时间。
9. Reaction Rate Graphs | 反应速率曲线图
Reaction progress is often shown as a graph of product amount (or reactant amount) against time. The gradient of the curve at any point gives the instantaneous rate.
反应进程常用产物量（或反应物量）对时间的曲线图来表示。曲线上任意一点的斜率给出瞬时速率。
At the start, the curve is steep because the rate is high. As reactants are used up, the gradient becomes less steep. Eventually the curve becomes flat when the reaction stops.
开始时曲线陡峭，因为速率高。随着反应物消耗，斜率变缓。最终反应停止时曲线变平坦。
10. Average vs Instantaneous Rate | 平均速率与瞬时速率
The average rate over the whole reaction is the total change in quantity divided by the total time taken.
整个反应的平均速率是总量变化除以所用总时间。
Average rate = Total change in amount ⁄ Total time
The instantaneous rate is the rate at a particular moment, found by drawing a tangent to the curve at that time and calculating its gradient.
瞬时速率是某一特定时刻的速率，通过在该时刻画切线并计算其斜率得到。
Instantaneous rates are more useful than average rates when studying how the reaction speeds up or slows down.
当研究反应如何加速或减速时，瞬时速率比平均速率更有用。
11. Real-World Applications | 实际应用
The factors affecting reaction rate have important everyday and industrial uses.
影响反应速率的因素在日常生活中以及工业上都有重要的应用。
Food preservation: low temperatures slow down spoilage reactions in food.
食品保鲜：低温减慢了食物中的变馊反应。
Digestion: enzymes act as biological catalysts to speed up digestion at body temperature.
消化：酶充当生物催化剂，在体温下加速消化。
Industry: powdered reactants are used instead of lumps, and catalysts are employed to increase production rates.
工业：使用粉状反应物代替块状，并采用催化剂来提高生产效率。
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