📚 Rates of Reaction | 化学反应速率
In this article, you will learn how to describe and measure the speed of a chemical reaction, explain why different factors affect this speed, and apply these ideas to industrial processes.
在这篇文章中，你将学习如何描述和测量化学反应的快慢，解释为什么不同因素会影响反应速度，并将这些概念应用于工业制程。
1. What is Rate of Reaction? | 什么是反应速率？
Rate of reaction tells us how fast a reaction happens. It can be defined as the decrease in the amount of a reactant or the increase in the amount of a product per unit time.
反应速率告诉我们反应发生的快慢。它可以定义为：单位时间内反应物数量的减少，或产物数量的增加。
Rate = change in quantity of reactant or product ÷ time
Common units are g/s, cm³/s, or mol/dm³/s. For example, if 24 cm³ of hydrogen gas is produced in 30 s, the average rate is 24 ÷ 30 = 0.8 cm³/s.
常用单位是 g/s、cm³/s 或 mol/dm³/s。例如，若 30 秒内产生 24 cm³ 氢气，则平均速率为 24 ÷ 30 = 0.8 cm³/s。
2. Measuring Rates | 测量速率
Several methods can be used to follow a reaction. The choice depends on the observable change.
测量反应速率的方法有很多，具体选择取决于反应中可观察到的变化。
-
If a gas is produced, collect it in a gas syringe and record the volume at regular time intervals.
如果有气体生成，可用气体注射器收集气体，并每隔一定时间记录体积。
-
If a gas escapes, measure the mass loss using a balance.
如果有气体逸出，可用天平测量质量减少。
-
If a precipitate forms, observe how quickly the mixture becomes cloudy.
如果生成沉淀，可以观察混合物变浑浊的快慢。
-
If there is a colour change, use a colorimeter or record the time to reach a colour mark.
如果发生颜色变化，可使用色度计或记录达到某一颜色标记所需的时间。
For example, magnesium reacting with hydrochloric acid produces hydrogen gas: Mg + 2HCl → MgCl₂ + H₂. The volume of H₂ can be measured every 10 seconds.
例如，镁与盐酸反应生成氢气：Mg + 2HCl → MgCl₂ + H₂。每 10 秒可测量一次 H₂ 的体积。
3. Collision Theory | 碰撞理论
For a reaction to occur, particles must collide with each other. However, not every collision is successful.
反应发生的必要条件是粒子之间发生碰撞。但并非每次碰撞都能引发反应。
A successful collision requires two conditions: the particles must have at least the activation energy, and they must collide with the correct orientation.
有效碰撞需要满足两个条件：粒子必须至少具有活化能，并且必须以正确的取向碰撞。
The rate of reaction depends on the frequency of successful collisions. Anything that increases the number of particles with enough energy, or increases how often they collide, will speed up the reaction.
反应速率取决于有效碰撞的频率。任何能增加具有足够能量粒子数量或增加碰撞频率的因素，都会加快反应。
4. Surface Area | 表面积
Breaking a solid into smaller pieces increases its surface area to volume ratio.
将固体粉碎成小块可以增大其表面积与体积之比。
For a given mass, powder has a much larger total surface area than large lumps. This means more solid particles are exposed to the other reactant, so collisions happen more often and the rate increases.
对于相同质量的固体，粉末的总表面积远大于大块固体。这意味着更多固体粒子暴露在另一种反应物中，因此碰撞更频繁，反应速率增大。
Consider marble chips reacting with hydrochloric acid: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. If the same mass of powdered marble is used, CO₂ is produced faster.
考虑大理石碎片与盐酸反应：CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂。若使用相同质量的粉末大理石，CO₂ 的产生会更快。
Rate ∝ surface area (for a fixed mass)
5. Temperature | 温度
Raising the temperature increases the average kinetic energy of particles.
升高温度会增加粒子的平均动能。
Particles move faster, so they collide more frequently. More importantly, a much larger fraction of particles have energy equal to or greater than the activation energy. This greatly increases the number of successful collisions.
粒子运动加快，碰撞更频繁。更重要的是，具有等于或大于活化能的粒子比例大大增加，从而显著提高有效碰撞次数。
As a rough rule, for many reactions the rate approximately doubles for every 10 °C rise in temperature.
粗略估计，对许多反应而言，温度每升高 10 °C，反应速率大约会翻倍。
For example, food spoils faster at room temperature than in a refrigerator because the bacteria-driven reactions are faster at higher temperatures.
例如，室温下食物比冰箱中更容易变质，因为在较高温度下，细菌引起的化学变化更快。
6. Concentration and Pressure | 浓度与压强
Increasing the concentration of a solution means more solute particles are present in the same volume.
增加溶液的浓度意味着相同体积内含有更多溶质粒子。
This increases the frequency of collisions between reactant particles, so the rate of reaction increases. For gases, increasing the pressure has the same effect as increasing concentration: particles are pushed closer together and collide more often.
这会增加反应物粒子间的碰撞频率，从而加快反应。对于气体，增大压强与增大浓度的效果相同：粒子被压缩得更紧密，碰撞更频繁。
In a reaction such as sodium thiosulfate + acid → sulfur + sodium sulfate + water, doubling the concentration of thiosulfate roughly doubles the rate at the start.
在硫代硫酸钠与酸的反应（生成硫、硫酸钠和水）中，将硫代硫酸盐浓度加倍通常会使初始速率大致加倍。
Rate ∝ concentration (often, for early part of reaction)
7. Catalysts | 催化剂
A catalyst is a substance that increases the rate of reaction without being used up. It provides an alternative reaction pathway with lower activation energy.
催化剂是一种能提高反应速率但自身不消耗的物质。它提供了活化能更低的另一条反应途径。
Because the activation energy is lower, a greater proportion of collisions are successful at the same temperature. The catalyst remains chemically unchanged at the end.
由于活化能降低，在相同温度下，更大比例的碰撞成为有效碰撞。反应结束时，催化剂在化学上保持不变。
For example, manganese(IV) oxide catalyses the decomposition of hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂.
例如，二氧化锰催化过氧化氢的分解：2H₂O₂ → 2H₂O + O₂。
In biological systems, enzymes are protein catalysts that are highly specific and work under mild conditions.
在生物体系中，酶是蛋白质催化剂，具有高度专一性，并在温和条件下起作用。
8. Reaction Profiles and Activation Energy | 反应过程图与活化能
Reaction profiles show the energy changes during a reaction.
反应过程图（能量曲线）展示反应过程中的能量变化。
In an exothermic reaction, the products have less energy than the reactants; the difference is released as heat. In an endothermic reaction, the products have more energy and energy is absorbed from the surroundings.
在放热反应中，产物能量低于反应物，差值以热量形式释放；在吸热反应中，产物能量高于反应物，能量从环境中吸收。
The activation energy is the minimum energy needed for reactants to form an activated complex or transition state. It is shown on the profile as the height of the energy barrier.
活化能是反应物形成活化配合物或过渡态所需的最低能量。在曲线上表现为能垒的高度。
Adding a catalyst lowers the activation energy by providing an alternative route, as shown by a second curve with a lower peak.
添加催化剂通过提供另一条途径降低活化能，在图中表现为具有较低峰值的新曲线。
9. Rates in Reversible Reactions | 可逆反应中的速率
In reversible reactions, the forward and backward reactions occur simultaneously once some product has formed.
在可逆反应中，一旦生成部分产物，正向和逆向反应便同时发生。
At equilibrium, the rates of the forward and backward reactions are equal, so the concentrations of reactants and products remain constant. This is called dynamic equilibrium.
当正逆反应速率相等时，反应物和产物的浓度保持不变，达到化学平衡，这称为动态平衡。
A catalyst speeds up both directions equally; it does not change the position of equilibrium, but it helps the system reach equilibrium faster.
催化剂同样加快正逆两个方向的速率，不会改变平衡位置，但能帮助体系更快地达到平衡。
Changing temperature, pressure or concentration can shift the position of equilibrium, but it does not change the fundamental rates until a new equilibrium is established.
改变温度、压强或浓度会改变平衡位置，但在新平衡建立之前，也会影响正逆反应的速率。
10. Applications in Industry | 工业应用
Industrial reactions are designed to give a profitable balance of rate and yield. Temperature, pressure, concentration and catalysts are chosen to maximise output with reasonable speed.
工业反应需要在速率和产率之间取得有利平衡。人们会选择适当的温度、压强、浓度和催化剂，以合理的速度最大化产量。
In the Haber process for ammonia: N₂ + 3H₂ ⇌ 2NH₃. A compromise temperature (about 450 °C), high pressure and an iron catalyst are used.
在哈伯法制氨中：N₂ + 3H₂ ⇌ 2NH₃。工业上采用约 450 °C 的折中温度、高压和铁催化剂。
In the contact process for sulfuric acid, vanadium(V) oxide is used as a catalyst to speed up the oxidation of SO₂ to SO₃.
在接触法制硫酸中，使用五氧化二钒作催化剂来加快 SO₂ 氧化为 SO₃ 的反应。
The table below summarises how changing conditions affects rate and yield in a reversible exothermic reaction such as ammonia synthesis.
下表总结了在类似合成氨这类可逆放热反应中，改变条件对速率和产率的影响。
| Condition | Effect on rate | Effect on yield |
| Increase temperature | Increases | 更多咨询请联系16621398022（同微信）
CommentsMore posts |
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply