A-Level Chemistry: Rates of Reaction – Key Points | A-Level 化学：反应速率 考点精讲

📚 A-Level Chemistry: Rates of Reaction – Key Points | A-Level 化学：反应速率 考点精讲

Reaction kinetics is a cornerstone of A-Level Chemistry, exploring how quickly chemical reactions occur and the factors that govern their speeds. Understanding reaction rates is essential not only for predicting yields in industrial processes but also for grasping fundamental concepts like activation energy, collision theory, and reaction mechanisms. This revision guide distils the key concepts, equations, and graphs you need to master rates of reaction.

反应动力学是 A-Level 化学的核心内容，它探讨化学反应进行的快慢以及控制反应速率的因素。理解反应速率不仅对预测工业过程的产率至关重要，也有助于掌握活化能、碰撞理论和反应机理等基本概念。本复习指南提炼了你需要掌握的反应速率关键概念、方程式和图像。

1. Defining Reaction Rate | 定义反应速率

The rate of a chemical reaction is defined as the change in concentration of a reactant or product per unit time. For a general reaction aA + bB → cC + dD, the rate can be expressed as:
Rate = −(1/a) Δ[A]/Δt = −(1/b) Δ[B]/Δt = (1/c) Δ[C]/Δt = (1/d) Δ[D]/Δt
The negative sign indicates consumption of reactants. Rate is typically measured in mol dm⁻³ s⁻¹.

化学反应速率定义为单位时间内反应物或生成物浓度的变化。对于一般反应 aA + bB → cC + dD，速率可表示为：
Rate = −(1/a)Δ[A]/Δt = −(1/b)Δ[B]/Δt = (1/c)Δ[C]/Δt = (1/d)Δ[D]/Δt
负号表示反应物的消耗。速率通常以 mol dm⁻³ s⁻¹ 为单位。

2. Measuring Reaction Rates | 测量反应速率

Several experimental methods can monitor the progress of a reaction and determine its rate:

• Gas collection: measuring volume of gas evolved over time (e.g., reaction of metals with acids).
• Mass loss: recording the decrease in mass as a gas escapes.
• Colorimetry: following colour change of a reactant or product using a spectrophotometer.
• pH monitoring: tracking pH changes in reactions involving acids or bases.
• Conductivity: measuring changes in ionic concentration.

有多种实验方法可以监测反应进程并确定其速率：

• 气体收集：测量随时间逸出气体的体积（如金属与酸的反应）。
• 质量减少：记录气体逸出时体系的质量减轻。
• 比色法：使用分光光度计跟踪反应物或产物的颜色变化。
• pH 监测：追踪涉及酸或碱的反应中 pH 的变化。
• 电导率：测量离子浓度的变化。

3. Collision Theory & Activation Energy | 碰撞理论与活化能

According to collision theory, for a reaction to occur, reactant particles must collide with sufficient kinetic energy (≥ activation energy, Eₐ) and with the correct orientation. Only effective collisions lead to product formation. The activation energy is the minimum energy barrier that must be overcome for a reaction to proceed. A higher Eₐ means fewer particles have enough energy, resulting in a slower rate at a given temperature.

根据碰撞理论，要发生反应，反应物粒子必须具有足够的动能（≥ 活化能, Eₐ）并以正确的取向碰撞。只有有效碰撞才能形成产物。活化能是反应进行所必须克服的最小能垒。Eₐ 越高，意味着具有足够能量的粒子越少，因此在给定温度下反应速率越慢。

4. Factors Affecting Reaction Rate | 影响反应速率的因素

The rate of a reaction is influenced by several factors:

• Concentration (solutions) or pressure (gases): higher concentration/pressure increases the number of particles per unit volume, leading to more frequent collisions. This does not change the energy distribution.
• Surface area of solids: increasing surface area exposes more particles to react, raising collision frequency.
• Temperature: raising temperature gives particles more kinetic energy, so a greater fraction of collisions exceed Eₐ. This is explained by the Maxwell-Boltzmann distribution.
• Catalysts: provide an alternative reaction pathway with a lower activation energy, increasing the proportion of successful collisions without being consumed.

反应速率受多种因素影响：

• 浓度（溶液）或压强（气体）：较高的浓度或压强增加了单位体积内粒子数，导致碰撞更频繁，但不改变能量分布。
• 固体的表面积：增大表面积使更多粒子暴露出来，提高了碰撞频率。
• 温度：升高温度使粒子动能增加，从而使超过 Eₐ 的碰撞比例增大。这可用麦克斯韦-玻尔兹曼分布解释。
• 催化剂：提供一条活化能较低的反应途径，增加有效碰撞的比例，而本身不被消耗。

5. Rate Equations & Order of Reaction | 速率方程与反应级数

For a reaction A + B → products, the rate equation has the form:
rate = k [A]ᵐ [B]ⁿ
where k is the rate constant, and m and n are the orders with respect to A and B, respectively. The overall order is m + n. The orders must be determined experimentally; they are not simply the stoichiometric coefficients. If m = 0, rate is independent of [A]; if m = 1, rate is directly proportional to [A]; if m = 2, rate is

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