Mastering Rate Equations and Activation Energy | 掌握速率方程与活化能

📚 Mastering Rate Equations and Activation Energy | 掌握速率方程与活化能

Kinetics is the branch of chemistry that explains how fast reactions occur. In Edexcel A-Level Chemistry, you must connect experimental rate measurements with rate equations, rate constants, activation energy and multi-step reaction mechanisms.

动力学是化学中解释反应快慢的分支。在 Edexcel A-Level Chemistry 中，你必须将实验速率测量与速率方程、速率常数、活化能以及多步反应机理联系起来。

1. Key Definitions in Kinetics | 动力学关键定义

Before using rate equations, you need secure definitions. The rate of reaction is the change in concentration of a reactant or product per unit time, with units mol dm⁻³ s⁻¹.

在使用速率方程之前，你需要掌握基本定义。反应速率是反应物或产物浓度在单位时间内的变化，单位为 mol dm⁻³ s⁻¹。

The order with respect to a species is the power to which its concentration is raised in the rate equation. Overall order is the sum of all individual orders.

对某物种的级数是指其浓度在速率方程中的幂。总级数是所有分级数之和。

2. Rate Equations and Orders | 速率方程与反应级数

For a reaction A + B → products, the rate equation is shown below. The powers m and n must be found experimentally; they are not generally the coefficients from the balanced equation.

对于反应 A + B → 产物，速率方程如下所示。幂 m 和 n 必须通过实验确定；它们通常不是配平方程中的系数。

Rate = k[A]ᵐ[B]ⁿ

The constant k is the rate constant, which changes with temperature but not with concentration. The powers m and n are the orders with respect to A and B.

常数 k 是速率常数，随温度变化，但不随浓度变化。幂 m 和 n 分别是 A 和 B 的级数。

3. Determining Orders from Experimental Data | 通过实验数据确定级数

Use the initial rates method: keep all concentrations constant except one, measure the initial rate, and compare changes. If doubling [A] doubles the rate, the order is first.

使用初始速率法：保持所有其他浓度不变，只改变一种物质的浓度，测量初始速率并进行比较。如果 [A] 翻倍使速率翻倍，则级数为一级。

If doubling [A] quadruples the rate, the order is second. If changing [A] has no effect, the order is zero. Always use initial rates because product build-up or reverse reactions can interfere later.

如果 [A] 翻倍使速率变为四倍，则级数为二级。如果 [A] 变化对速率无影响，则级数为零级。始终使用初始速率，因为产物积累或逆反应会在后期产生干扰。

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

The units of k depend on overall order. A quick way to find them is to rearrange the rate equation so k is the subject: k = Rate / ([A]ᵐ[B]ⁿ).

k 的单位取决于总级数。一种快速推导方法是将速率方程重排，使 k 成为主体：k = Rate / ([A]ᵐ[B]ⁿ)。