Rate of Reaction and Its Influencing Factors | 化学反应速率及其影响因素

📚 Rate of Reaction and Its Influencing Factors | 化学反应速率及其影响因素

The rate of a chemical reaction measures how quickly reactants are converted into products. This article explores the definition of reaction rate, methods of measurement, and five key factors that influence how fast reactions proceed, all within the IB Chemistry Diploma Programme.

化学反应速率衡量的是反应物转化为产物的快慢。本文将探讨反应速率的定义、测量方法，以及影响反应速率的五大关键因素，完全对标 IB 化学文凭课程大纲。

---

1. What is Reaction Rate? | 什么是反应速率

Reaction rate is defined as the change in concentration of a reactant or product per unit time. It is expressed in units of mol dm⁻³ s⁻¹, and can be written as the rate of disappearance of a reactant or the rate of appearance of a product.

反应速率定义为反应物或产物浓度随时间的变化量，单位为 mol dm⁻³ s⁻¹，既可以用反应物的消耗速率表示，也可以用产物的生成速率表示。

For a general reaction A → B, the rate can be expressed using the following equation:

对于一般反应 A → B，速率可用以下方程表示：

Rate = −Δ[A]/Δt = Δ[B]/Δt

The negative sign in front of Δ[A] indicates that the concentration of reactant A decreases over time, making the rate a positive quantity. Since Δ[B] increases, no sign change is needed.

Δ[A] 前的负号表示反应物 A 的浓度随时间减少，使速率保持正值；而 Δ[B] 是增加的，因此无需加负号。

It is important to note that reaction rates are not constant throughout a reaction. As reactants are consumed, the rate typically decreases because collisions become less frequent.

需要注意，反应速率在整个反应过程中并非恒定值。随着反应物被消耗，碰撞频率降低，速率通常会逐渐减慢。

---

2. Measuring Reaction Rate | 测量反应速率

Several experimental techniques are used to monitor reaction rates in the IB laboratory, depending on the physical or chemical properties that change during the reaction.

在 IB 实验中，根据反应过程中物理或化学性质的变化，可以采用多种实验技术来监测反应速率。

• Gas volume measurement: Use a gas syringe or measuring cylinder to record the volume of gas produced over time, for example in the reaction between magnesium and hydrochloric acid.

  气体体积测量：使用气体注射器或量筒记录气体随时间产生的体积，例如镁与盐酸的反应。

• Mass loss measurement: Use a balance to record the decrease in mass when a gaseous product escapes, such as in the decomposition of calcium carbonate with acid.

  质量损失测量：使用天平记录气体逸出引起的质量减少，例如碳酸钙与酸的反应。

• Colorimetry: Measure the intensity of colour to track the concentration of a coloured species, such as the iodine clock reaction.

  比色法：通过颜色强度变化追踪有色物质的浓度，例如碘钟反应。

The choice of method depends on the reaction. A primary requirement is that the measured property changes significantly and can be recorded quickly and accurately.

测量方法的选择取决于反应本身。关键是所测性质变化显著，且能够快速、准确地记录。

---

3. Collision Theory | 碰撞理论

Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy and with the correct orientation. Only collisions that meet these two criteria — called effective collisions — lead to product formation.

碰撞理论指出，反应发生的必要条件是反应物粒子发生碰撞，且必须具有足够的能量和正确的取向。只有满足这两个条件的碰撞——称为有效碰撞——才能生成产物。

The minimum energy that colliding particles must possess to break existing bonds is called the activation energy (Eₐ). The fraction of particles with energy equal to or greater than Eₐ can be visualised using a Maxwell-Boltzmann distribution curve.

碰撞粒子为断裂既有化学键所需的最低能量称为活化能（Eₐ）。能量大于或等于 Eₐ 的粒子比例可用麦克斯韦-玻尔兹曼分布曲线来直观表示。

Effective collision = sufficient energy + correct orientation

有效碰撞 = 足够的能量 + 正确的取向

Any factor that increases the frequency of effective collisions will increase the rate of reaction. This principle underlies all the factors discussed in this article.

任何能够提高有效碰撞频率的因素都会加快反应速率。这一原理是本文所讨论所有影响因素的基础。

---

4. Effect of Concentration | 浓度的影响

For solutions, increasing the concentration of reactants increases the number of particles per unit volume. This leads to a higher frequency of collisions per second, and therefore a higher proportion of effective collisions overall.

对于溶液而言，增加反应物浓度会增大单位体积内的粒子数目，导致每秒碰撞频率升高，有效碰撞的总比例也随之增大，从而加快反应速率。

The IB course does not require the full rate expression for every reaction, but a qualitative understanding is essential. For many simple reactions, rate is directly proportional to concentration of a particular reactant: doubling the concentration approximately doubles the number of collisions per unit time.

IB 课程不要求对每个反应都写出完整速率表达式，但定性的理解至关重要。对许多简单反应而言，速率与某一反应物浓度成正比：浓度加倍时，单位时间内的碰撞次数也大约加倍。

Experimentally, one can mix different concentrations of sodium thiosulfate with hydrochloric acid and measure the time taken for a cross drawn on paper to disappear due to the precipitated sulfur.

实验中，可以将不同浓度的硫代硫酸钠与盐酸混合，记录纸上画叉消失所需的时间——消失越快，说明硫沉淀生成越快，反应速率越高。

---

5. Effect of Surface Area | 表面积的影响

For solids, the reaction occurs at the solid surface where particles are exposed to the other reactant. Grinding a solid into smaller pieces increases its total surface area, exposing more particles to the reacting medium.

对于固体，反应发生在固体的表面，即粒子暴露于另一反应物的位置。将固体磨成更小的颗粒会增大其总表面积，使更多粒子暴露在反应介质中。

• Increase in surface area → more exposed particles → higher collision frequency → faster reaction.

  表面积增大 → 暴露粒子增多 → 碰撞频率升高 → 反应加快。

• Decrease in particle size → increase in surface area-to-volume ratio → faster reaction.

  粒径减小 → 表面积与体积之比增大 → 反应加快。

For example, powdered calcium carbonate reacts with hydrochloric acid much faster than marble chips of equal mass, because the powder presents a far larger contact area to the acid.

例如，粉末状碳酸钙与盐酸反应的速率远快于等质量的石灰石颗粒，因为粉末提供了更大的接触面积。

---

6. Effect of Temperature | 温度的影响

Raising temperature increases the average kinetic energy of particles, causing them to move faster and collide more frequently. More importantly, a greater proportion of particles now possess energy equal to or above the activation energy Eₐ.

升高温度会增加粒子的平均动能，使粒子运动更快、碰撞更频繁。更重要的是，能量达到或超过活化能 Eₐ 的粒子比例显著增大。

A general rule of thumb is that the rate of reaction approximately doubles for every 10 °C rise in temperature. This is because the relationship between temperature and the fraction of particles exceeding Eₐ is exponential.

经验规律是：温度每升高 10 °C，反应速率大约翻一倍。这是因为温度与超过 Eₐ 的粒子比例之间存在指数关系。

On a Maxwell-Boltzmann distribution curve, raising the temperature shifts the curve to the right and makes it flatter. The area under the curve to the right of Eₐ increases, meaning more particles can react on collision.

在麦克斯韦-玻尔兹曼分布曲线上，升高温度使曲线向右移动并变得扁平。曲线在 Eₐ 右侧的面积增大，意味着更多粒子能在碰撞时发生反应。

Fraction of particles above Eₐ increases exponentially with temperature

超过 Eₐ 的粒子比例随温度呈指数增长

This explains why reactions that are slow at room temperature may proceed rapidly when heated, even though the temperature increase provides only a modest rise in average kinetic energy.

这解释了为什么室温下很慢的反应在加热后会快速进行——尽管温度升高对平均动能的提升幅度并不大。

---

7. Effect of Pressure (Gases) | 压强的影响（气体）

For reactions involving gases, increasing the pressure decreases the volume occupied by a fixed amount of gas, which increases the concentration of gas particles. The particles are packed more closely and collide more frequently.

对于涉及气体的反应，增大压强会使固定量气体所占体积减小，气体粒子浓度增大。粒子排列更紧密，碰撞频率更高。

Pressure affects the rate of gaseous reactions in exactly the same way that concentration affects solution reactions — by increasing the number of effective collisions per unit time.

压强对气态反应速率的影响与浓度对溶液反应的影响方式完全一致——都是通过增加单位时间内的有效碰撞次数来实现的。

Higher pressure → higher gas concentration → higher collision frequency → faster rate

压强增大 → 气体浓度升高 → 碰撞频率增大 → 速率加快

It is worth noting that pressure has a negligible effect on reactions involving only solids and liquids, because these phases are essentially incompressible.

需要指出的是，压强对仅涉及固体和液体的反应影响可忽略不计，因为这些相几乎不可压缩。

---

8. Effect of Catalysts | 催化剂的影响

A catalyst is a substance that increases the rate of a reaction without being consumed in the overall reaction. It works by providing an alternative reaction pathway with a lower activation energy.

催化剂是一种能加快反应速率但不参与最终消耗的物质。它通过提供一条活化能更低的反应路径来起作用。

With a lower activation energy, a larger fraction of particles has sufficient energy to react at a given temperature. Consequently, the rate of reaction increases without any change in temperature or concentration.

活化能降低后，在相同温度下，拥有足够能量发生反应的粒子比例增大。因此，无需改变温度或浓度，反应速率也能提高。

Catalyst lowers Eₐ → more particles exceed Eₐ → faster reaction

催化剂降低 Eₐ → 超过 Eₐ 的粒子增多 → 反应加快

Key features of catalysts in IB chemistry:

IB 化学中催化剂的关键特征：

• Catalysts are specific: different reactions require different catalysts.

  催化剂具有特异性：不同反应需要不同催化剂。

• Catalysts do not affect the position of equilibrium, only the time taken to reach it.

  催化剂不影响平衡位置，只影响达到平衡所需的时间。

• Catalysts are not used up; they can be recovered chemically unchanged at the end of the reaction.

  催化剂不会被消耗；反应结束时可以化学形式原样回收。

---

9. Activation Energy and the Maxwell-Boltzmann Distribution | 活化能与麦克斯韦-玻尔兹曼分布

The Maxwell-Boltzmann distribution curve plots the number of particles against their kinetic energy. It shows that at any given temperature, the majority of particles have intermediate energies, while only a small fraction possess very high energy.

麦克斯韦-玻尔兹曼分布曲线以粒子数目为纵轴、动能为横轴，展示在任何给定温度下，大多数粒子具有中等能量，仅一小部分粒子拥有很高的能量。

For a reaction with activation energy Eₐ, the area under the curve to the right of Eₐ corresponds to the fraction of collisions that possess sufficient energy to react. This area can be increased either by raising the temperature or by adding a catalyst.

对于活化能为 Eₐ 的反应，曲线在 Eₐ 右侧的面积对应着能量足以反应的碰撞比例。这一面积既可以通过升高温度增大，也可以通过添加催化剂增大。

Comparison of two temperatures:

两种温度的比较：

Property | 性质	Low temperature | 低温	High temperature | 高温
Average kinetic energy | 平均动能	Lower | 较低	Higher | 较高
Peak of distribution curve | 分布曲线峰值	Higher and to the left | 更高且偏左	Lower and to the right | 更低且偏右
Fraction of particles exceeding Eₐ | 超过 Eₐ 的粒子比例	Small | 小	Large | 大

By contrast, adding a catalyst does not change the shape or position of the distribution curve at all. It simply lowers the activation energy line, so a larger area of the same curve lies to the right of the new Eₐ.

相比之下，添加催化剂完全不会改变分布曲线的形状或位置。它只是将活化能线降低，使同一条曲线在新生 Eₐ 右侧的面积增大。

---

10. Summary and Exam Tips | 总结与考试要点

Published by TutorHao | IB Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）