IB Chemistry: Core Concepts of Chemical Kinetics | IB化学：化学动力学核心知识梳理

📚 IB Chemistry: Core Concepts of Chemical Kinetics | IB化学：化学动力学核心知识梳理

Chemical kinetics is the branch of chemistry that deals with the rates of chemical reactions and the mechanisms by which they occur. In IB Chemistry, understanding kinetics allows you to predict how fast reactions proceed, interpret rate data, and explain how different conditions affect reaction speed.

化学动力学是化学中研究化学反应速率以及反应发生机理的分支。在IB化学中，理解动力学能够帮助你预测反应进行的快慢、解读速率数据，并解释不同条件如何影响反应速率。

1. Rate of Reaction | 反应速率

The rate of a reaction is defined as the change in concentration of a reactant or product per unit time. It is usually expressed in mol dm⁻³ s⁻¹. For a reactant A, the rate is negative because its concentration decreases; for a product, it is positive.

反应速率定义为反应物或生成物浓度随时间的变化量，通常以 mol dm⁻³ s⁻¹ 为单位。对于反应物 A，其浓度减小，速率取负值；对于生成物，速率取正值。

For a general reaction aA + bB → cC + dD, the rate can be written as:

对于一般反应 aA + bB → cC + dD，速率可以写为：

Rate = −(1/a)Δ[A]/Δt = −(1/b)Δ[B]/Δt = (1/c)Δ[C]/Δt = (1/d)Δ[D]/Δt

The average rate is calculated over a time interval, while the instantaneous rate is the slope of the tangent at a specific time on a concentration–time graph.

平均速率是在一段时间间隔内计算的，而瞬时速率是浓度-时间图上某一点切线的斜率。

2. Rate Expression and Order of Reaction | 速率表达式与反应级数

The rate expression (or rate law) relates the rate of a reaction to the concentrations of reactants, each raised to a power. For the reaction aA + bB → products, the experimental rate expression is:

速率表达式（或速率定律）将反应速率与各反应物浓度的幂次关联起来。对于反应 aA + bB → 产物，实验测得的速率表达式为：

Rate = k[A]^m[B]ⁿ

Here, k is the rate constant, m is the order with respect to A, and n is the order with respect to B. The overall order is m + n. The orders are not necessarily equal to the stoichiometric coefficients; they must be determined experimentally.

其中 k 是速率常数，m 是相对于 A 的反应级数，n 是相对于 B 的反应级数。总反应级数为 m + n。反应级数不一定等于化学计量系数，必须通过实验确定。

Zero order: Rate = k (constant), independent of reactant concentration.
零级反应：Rate = k（常数），与反应物浓度无关。
First order: Rate = k[A], rate proportional to [A].
一级反应：Rate = k[A]，速率与 [A] 成正比。
Second order: Rate = k[A]², or Rate = k[A][B].
二级反应：Rate = k[A]²，或 Rate = k[A][B]。

3. Determining Reaction Orders | 测定反应级数

Reaction orders are determined by the initial rates method or by using integrated rate laws and concentration–time graphs. In the initial rates method, you change the concentration of one reactant while keeping others constant and compare the initial rates.

反应级数可通过初始速率法或利用积分速率定律和浓度-时间图来确定。在初始速率法中，保持其他反应物浓度不变，只改变一种反应物的浓度，并比较初始速率。

If doubling [A] doubles the rate while [B] is held constant, the reaction is first order in A. If doubling [A] quadruples the rate, it is second order in A. If the rate remains unchanged, it is zero order in A.

如果保持 [B] 不变，将 [A] 加倍使速率加倍，则反应对 A 是一级；如果将 [A] 加倍使速率变为四倍，则对 A 是二级；如果速率不变，则对 A 是零级。

For a first-order reaction, a graph of ln[A] versus t gives a straight line with slope −k. For a second-order reaction, a graph of 1/[A] versus t is linear with slope k.

对于一级反应，ln[A] 对 t 作图得到斜率为 −k 的直线；对于二级反应，1/[A] 对 t 作图呈直线，斜率为 k。

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

The rate constant k is a proportionality constant that depends on temperature and the presence of a catalyst. It is constant for a given reaction at a fixed temperature. The units of k depend on the overall order of the reaction.

速率常数 k 是一个比例常数，取决于温度和催化剂的存在。在固定温度下，对给定反应它是一个常数。k 的单位取决于反应的总级数。

For a reaction with overall order n, the units of k are (mol dm⁻³)¹⁻ⁿ s⁻¹. For a zero-order reaction, k has units mol dm⁻³ s⁻¹. For first order, k has units s⁻¹. For second order, k has units dm³ mol⁻¹ s⁻¹.

对于总级数为 n 的反应，k 的单位为 (mol dm⁻³)¹⁻ⁿ s⁻¹。零级反应的 k 单位是 mol dm⁻³ s⁻¹；一级反应是 s⁻¹；二级反应是 dm³ mol⁻¹ s⁻¹。

5. Collision Theory and Activation Energy | 碰撞理论与活化能

Collision theory states that for a reaction to occur, particles must collide with sufficient energy and correct orientation. Only a small fraction of collisions are effective enough to lead to product formation.

碰撞理论认为，反应发生的条件是粒子必须具有足够的能量并以正确的取向碰撞。只有一小部分碰撞有效到足以生成产物。

The minimum energy required for an effective collision is called the activation energy, Eₐ. This energy is needed to break or weaken existing bonds and form the transition state (activated complex).

有效碰撞所需的最小能量称为活化能 Eₐ。该能量用于断裂或削弱已有化学键，并形成过渡态（活化配合物）。

Rate ∝ collision frequency × fraction of effective collisions

速率 ∝ 碰撞频率 × 有效碰撞比例

6. Maxwell–Boltzmann Distribution | 麦克斯韦-玻尔兹曼分布

The Maxwell–Boltzmann distribution shows the spread of energy among particles in a sample at a given temperature. The area under the curve represents the total number of particles, and the shaded region beyond Eₐ represents particles with energy equal to or greater than the activation energy.

麦克斯韦-玻尔兹曼分布显示在给定温度下样品中粒子能量的分布。曲线下的面积代表粒子总数，超过 Eₐ 的阴影区域代表能量等于或大于活化能的粒子。

Increasing the temperature shifts the distribution curve to the right and flattens it, increasing the fraction of particles with energy above Eₐ. This explains why reaction rates increase sharply with temperature.

升高温度会使分布曲线向右移动并变得平坦，从而增加能量高于 Eₐ 的粒子比例。这就解释了为什么反应速率随温度升高而急剧增加。

Adding a catalyst lowers Eₐ, allowing a larger fraction of particles to have sufficient energy, thereby increasing the rate without changing the temperature.

加入催化剂会降低 Eₐ，使更大比例的粒子具有足够能量，从而在温度不变的条件下提高速率。

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

Key factors include concentration, temperature, surface area, pressure (for gases), and catalysts. Each affects the rate by altering collision frequency or the fraction of effective collisions.

关键因素

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IB Chemistry: Core Concepts of Chemical Kinetics | IB化学：化学动力学核心知识梳理