Edexcel A-Level Chemistry Topic 16: Kinetics II | Edexcel A-Level 化学第16讲：化学动力学(二)

📚 Edexcel A-Level Chemistry Topic 16: Kinetics II | Edexcel A-Level 化学第16讲：化学动力学(二)

In Edexcel A-Level Chemistry, Topic 16 (Kinetics II) extends the basic collision theory ideas from AS-level into the quantitative treatment of reaction rates. You will learn how to write rate equations, determine reaction orders experimentally, deduce rate constants and their units, link mechanisms to the rate-determining step, and use the Arrhenius equation to explain the effect of temperature and catalysts on rate. This article covers the key concepts, equations and exam techniques needed for success.

在 Edexcel A-Level 化学中，第16讲（化学动力学二）从 AS 阶段的碰撞理论延伸至反应速率的定量处理。你将学习如何书写速率方程、通过实验确定反应级数、推导速率常数及其单位、将反应机理与决速步骤联系起来，并用阿伦尼乌斯方程解释温度和催化剂对速率的影响。本文涵盖关键概念、公式和考试技巧，帮助你从容应对考试。

1. Rate Equations and Rate Constants | 速率方程与速率常数

The rate of a chemical reaction is often expressed as a rate equation: rate = k[A]ᵐ[B]ⁿ. Here [A] and [B] are the concentrations of reactants, m and n are the orders of reaction with respect to A and B, and k is the rate constant. The values of m and n are not necessarily equal to the stoichiometric coefficients in the balanced equation; they must be determined experimentally.

化学反应速率常表示为速率方程：rate = k[A]ᵐ[B]ⁿ。其中 [A] 和 [B] 是反应物浓度，m 和 n 分别是反应对 A 和 B 的级数，k 是速率常数。m 和 n 不一定等于配平方程中的化学计量数，必须由实验确定。

The overall order of reaction is the sum m + n. Orders may be zero, first order, second order or, less commonly, fractional. A zero-order reaction has a rate that is independent of the concentration of that reactant, whereas a first-order reaction has a rate directly proportional to the concentration.

总反应级数为 m + n 之和。级数可以为零级、一级、二级，少数情况下还可能出现分数级数。零级反应的速率与该反应物浓度无关；一级反应的速率则与该反应物浓度成正比。

rate = k[A]ᵐ[B]ⁿ

2. Determining Reaction Orders | 确定反应级数

The initial rates method is the most common way to find reaction orders. You measure the initial rate of reaction for several experiments in which only one reactant concentration is changed while others are kept constant. By comparing how the initial rate changes when, say, [A] doubles, you can deduce the order with respect to A.

初始速率法是确定反应级数最常用的方法。你在若干次实验中只改变一种反应物的浓度，保持其余反应物浓度不变，并测量反应的初始速率。通过比较当例如 [A] 加倍时初始速率如何变化，即可推断该反应对 A 的级数。

If doubling [A] doubles the rate, the reaction is first order in A. If doubling [A] quadruples the rate, the reaction is second order in A. If changing [A] has no effect on the rate, it is zero order in A. The same logic applies when [B] is varied while [A] is kept constant.

如果 [A] 加倍时速率加倍，则反应对 A 为一级；如果 [A] 加倍时速率变为原来的四倍，则对 A 为二级；如果改变 [A] 对速率没有影响，则对 A 为零级。当保持 [A] 不变而改变 [B] 时，同样

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