Edexcel A-Level Chemistry 16.1: Rate Equations and Orders of Reaction | 爱德思A-Level化学16.1：速率方程与反应级数

📚 Edexcel A-Level Chemistry 16.1: Rate Equations and Orders of Reaction | 爱德思A-Level化学16.1：速率方程与反应级数

In Edexcel A-Level Chemistry, the rate of a reaction is not always linked to the balanced equation in a simple way. The rate equation shows how the initial rate depends on the concentrations of specific reactants, with each concentration raised to a power called the order of reaction. These orders must be found by experiment and are central to understanding reaction kinetics.

在爱德思 A-Level 化学中，反应速率并不总是以简单方式与配平方程式相联系。速率方程展示了初始速率如何取决于特定反应物的浓度，每个浓度都有一个幂次，称为反应级数。这些级数必须通过实验确定，是理解反应动力学的核心。

1. The Rate Equation: An Overview | 速率方程概述

For a general reaction such as A + B → products, the experimental rate equation can be written as rate = k[A]ᵐ[B]ⁿ. Here k is the rate constant, while m and n are the orders of reaction with respect to A and B. The overall order is the sum m + n.

对于 A + B → 产物 这类一般反应，实验测得的速率方程可写为 rate = k[A]ᵐ[B]ⁿ。其中 k 是速率常数，m 和 n 分别是对 A 和 B 的反应级数。总反应级数是 m + n 之和。

It is important to remember that m and n are usually 0, 1 or 2. They are not automatically equal to the stoichiometric coefficients in the balanced equation. Only for an elementary reaction, which occurs in a single step, do the orders match the stoichiometric coefficients.

必须记住，m 和 n 通常为 0、1 或 2。它们并不自动等于配平方程式中的化学计量数。只有当反应是基元反应，即一步完成时，级数才与化学计量数一致。

2. Order of Reaction Explained | 反应级数解析

Zero order means the rate is independent of the concentration of that reactant. Changing the concentration has no effect on the rate, so rate = k[A]⁰ = k. This often occurs when a catalyst or a surface is saturated.

零级意味着反应速率与该反应物浓度无关。改变浓度对速率没有影响，因此 rate = k[A]⁰ = k。这通常发生在催化剂或表面饱和时。

First order means the rate is directly proportional to the concentration. If you double the concentration, the rate doubles. Second order means the rate is proportional to the square of the concentration. Doubling the concentration multiplies the rate by 2² = 4.

一级意味着速率与浓度成正比。若浓度加倍，速率加倍。二级意味着速率与浓度的平方成正比。浓度加倍会使速率乘以 2² = 4。

• Zero order: rate unchanged when concentration changes
• First order: rate doubles when concentration doubles
• Second order: rate quadruples when concentration doubles

• 零级：浓度改变时速率不变
• 一级：浓度加倍时速率加倍
• 二级：浓度加倍时速率变为四倍

3. How to Deduce Orders from Experimental Data | 如何通过实验数据推断反应级数

The most common method is the initial rates method. You compare two experiments where only one concentration changes while all other concentrations stay constant. Then you compare the change in initial rate with the change in that concentration.

最常用的方法是初始速率法。比较两个实验，其中只有一个浓度改变，而其他浓度保持不变。然后比较初始速率的变化与该浓度的变化。

If the rate ratio equals the concentration ratio, the order is 1. If the rate ratio equals the concentration ratio squared, the order is 2. If the rate does not change, the order is 0.

如果速率比等于浓度比，则级数为 1。如果速率比等于浓度比的平方，则级数为 2。如果速率不变，则级数为 0。

4. The Rate Constant k and Its Units | 速率常数 k 及其单位

The rate constant k is a proportionality constant for a given reaction at a fixed temperature. Its value changes with temperature but not with concentration. The units of k depend on the overall order of reaction.

速率常数 k 是给定反应在固定温度下的比例常数。其数值随温度变化，但不随浓度变化。k 的单位取决于反应的总级数。