📚 AQA A-Level Chemistry 1.6 Kinetics | AQA A-Level 化学 1.6 反应动力学
Welcome to this AQA A-Level Chemistry revision guide for Topic 1.6 Kinetics. This topic explains why some reactions are fast, some are slow, and how we can control reaction rates.
欢迎阅读本 AQA A-Level 化学 1.6 动力学复习指南。本主题解释为什么有些反应快、有些反应慢，以及我们如何控制反应速率。
You will learn about collision theory, activation energy, the Maxwell-Boltzmann distribution, and the effects of temperature, concentration, pressure and catalysts.
你将学习碰撞理论、活化能、麦克斯韦-玻尔兹曼分布，以及温度、浓度、压强和催化剂的影响。
1. Collision Theory | 碰撞理论
Collision theory states that for a chemical reaction to occur, reactant particles must collide with each other.
碰撞理论指出，要发生化学反应，反应物粒子必须相互碰撞。
However, only a small fraction of collisions actually lead to a chemical change. A successful collision must satisfy two conditions: the colliding particles must have kinetic energy greater than or equal to the activation energy, and they must collide with the correct orientation.
然而，只有一小部分碰撞实际上会引发化学变化。一次有效碰撞必须满足两个条件：碰撞粒子的动能必须大于或等于活化能，并且必须以正确的方向碰撞。
The rate of a reaction therefore depends on the frequency of collisions and the fraction of collisions that are successful.
因此，反应速率取决于碰撞频率和有效碰撞所占的比例。
rate = Z × f × p
In this expression, Z is the collision frequency, f is the fraction of collisions with sufficient energy, and p is the orientation or steric factor.
在该表达式中，Z 是碰撞频率，f 是具有足够能量的碰撞比例，p 是取向因子或空间因子。
2. Activation Energy | 活化能
Activation energy, Eₐ, is the minimum energy required for a collision to result in a chemical reaction.
活化能 Eₐ 是碰撞能够引发化学反应所需的最低能量。
When reactant particles collide with energy below Eₐ, they simply bounce apart without reacting. Only collisions with energy equal to or greater than Eₐ can break existing bonds and allow new bonds to form.
当反应物粒子以低于 Eₐ 的能量碰撞时，它们只会弹开而不发生反应。只有能量等于或大于 Eₐ 的碰撞才能断裂旧键并形成新键。
Reactions with high activation energies tend to be slower because fewer particles have enough energy to react at a given temperature.
活化能高的反应通常较慢，因为在给定温度下具有足够能量的粒子较少。
The activation energy is an energy barrier that must be overcome before reactant particles can become products.
活化能是反应物粒子在转变为产物之前必须克服的能量壁垒。
3. Maxwell-Boltzmann Distribution | 麦克斯韦-玻尔兹曼分布
The Maxwell-Boltzmann distribution shows the distribution of kinetic energies among molecules in a gas or liquid at a given temperature.
麦克斯韦-玻尔兹曼分布显示了在给定温度下气体或液体中分子的动能分布。
The curve starts at the origin, rises to a peak at the most probable energy, and then decreases gradually towards high energies. The area under the curve represents the total number of molecules.
曲线从原点开始，上升到最概然能量处出现峰值，然后向高能方向逐渐下降。曲线下的面积代表分子的总数。
The high-energy tail of the curve is important in kinetics: only molecules with kinetic energy greater than or equal to Eₐ can react when they collide.
曲线的高能尾部在动力学中很重要：只有动能大于或等于 Eₐ 的分子才能在碰撞时发生反应。
of molecules with E ≥ Eₐ is given by the area under the curve to the right of the Eₐ line.
能量 E ≥ Eₐ 的分子比例由 Eₐ 线右侧曲线下的面积表示。
4. Effect of Temperature on Reaction Rate | 温度对反应速率的影响
Increasing the temperature increases the average kinetic energy of the reactant particles, so they move faster and collide more frequently.
升高温度会增加反应物粒子的平均动能，因此它们运动更快，碰撞更频繁。
More importantly, the Maxwell-Boltzmann curve shifts to the right and becomes flatter, so a much larger proportion of molecules have kinetic energy greater than or equal to Eₐ.
更重要的是，麦克斯韦-玻尔兹曼曲线向右移动并变得更加平坦，因此具有大于或等于 Eₐ 动能的分子比例大大增加。
This is why a small rise in temperature often produces a large increase in reaction rate: the number of successful collisions rises sharply.
这就是为什么温度小幅升高往往会使反应速率大幅增加：有效碰撞次数急剧上升。
Raising the temperature does not lower the activation energy; it simply increases the proportion of particles that can exceed the existing Eₐ.
升高温度并不会降低活化能；它只是增加了能够超过原有 Eₐ 的粒子比例。
5. Effect of Concentration on Reaction Rate | 浓度对反应速率的影响
For reactions in solution, increasing the concentration of a reactant means there are more reactant particles per unit volume.
对于溶液中的反应，增加反应物浓度意味着单位体积内有更多的反应物粒子。
This increases the collision frequency between reactant particles, so successful collisions occur more often per unit time and the rate increases.
这会增加反应物粒子之间的碰撞频率，因此单位时间内有效碰撞更频繁地发生，速率增大。
The Maxwell-Boltzmann distribution itself does not change shape when concentration changes, because the energy distribution depends on temperature, not concentration.
当浓度改变时，麦克斯韦-玻尔兹曼分布本身的形状不会改变，因为能量分布取决于温度，而不是浓度。
Instead, concentration affects the total number of particles available to collide, which is equivalent to increasing Z in the rate expression.
相反，浓度影响可用于碰撞的粒子总数，这相当于增大速率表达式中的 Z。
6. Effect of Pressure on Reaction Rate | 压强对反应速率的影响
For reactions involving gases, increasing the pressure at constant temperature pushes gas particles closer together.
对于涉及气体的反应，在恒温下增加压强会使气体粒子靠得更近。
This raises the number of molecules per unit volume and therefore increases collision frequency, leading to a faster reaction.
这会增加单位体积内的分子数，从而增加碰撞频率，使反应加快。
An increase in pressure has the same effect on rate as an increase in concentration for gaseous reactants.
对于气体反应物，增加压强与增加浓度对速率的影响相同。
Again, the shape of the Maxwell-Boltzmann distribution is unchanged by pressure alone; only the collision frequency increases.
同样，仅压强改变不会改变麦克斯韦-玻尔兹曼分布的形状；只有碰撞频率增加。
7. Catalysts: Definition and Types | 催化剂：定义与类型
A catalyst is a substance that increases the rate of a chemical reaction without being used up in the overall process.
催化剂是一种能提高化学反应速率而在整个过程中本身不被消耗的物质。
Catalysts work by providing an alternative reaction pathway with a lower activation energy.
催化剂通过提供活化能较低的另一条反应路径来发挥作用。
There are two main types: homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase, usually solid with gaseous or liquid reactants.
催化剂主要有两类：均相催化剂与反应物处于同一相；非均相催化剂与反应物处于不同相，通常是固体与气体或液体反应物。
Common examples include iron in the Haber process, vanadium(V) oxide in the Contact process, and enzymes in biological systems.
常见例子包括哈伯法中的铁、接触法中的五氧化二钒，以及生物体系中的酶。
8. How Catalysts Increase Reaction Rate | 催化剂如何提高反应速率
Because a catalyst lowers the activation energy, a larger proportion of reactant particles have enough energy to react at the same temperature.
由于催化剂降低了活化能，在相同温度下，具有足够能量发生反应的反应物粒子比例更大。
This is shown on a Maxwell-Boltzmann diagram by moving the Eₐ line to the left; the area under the curve to the right of the new Eₐ is much larger.
这在麦克斯韦-玻尔兹曼图中表现为 Eₐ 线向左移动；新 Eₐ 右侧的曲线下面积要大得多。
The catalyst does not shift the Maxwell-Boltzmann distribution itself and does not increase the kinetic energy of the particles.
催化剂本身不会移动麦克斯韦-玻尔兹曼分布，也不会增加粒子的动能。
Instead, it makes a greater fraction of the existing
Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图