Rates of Reaction | 反应速率

📚 Rates of Reaction | 反应速率

The rate of reaction describes how quickly reactants are converted into products. In IGCSE Science (Edexcel), you need to understand how to measure rates, explain them using collision theory, and apply the factors that alter them.

反应速率描述反应物转化为产物的快慢。在 Edexcel IGCSE 科学中，你需要理解如何测量速率、用碰撞理论解释速率，并掌握改变速率的因素。

1. What is Rate of Reaction? | 什么是反应速率

The rate of reaction is the change in amount of a reactant or product per unit time. It can be expressed as an average rate over a period of time, or as an instantaneous rate at a particular moment.

反应速率是单位时间内反应物或产物物质量的变化。它既可以表示某段时间内的平均速率，也可以表示某一瞬间的瞬时速率。

For example, when magnesium reacts with hydrochloric acid, the mass of the mixture decreases because hydrogen gas escapes. The faster the mass drops, the faster the reaction.

例如，镁与盐酸反应时，由于氢气逸出，混合物的质量减少。质量下降得越快，反应就越快。

Average rate = total change in quantity ÷ total time taken
平均速率 = 总量变化 ÷ 总时间

2. Measuring Reaction Rates | 测定反应速率

Common methods for measuring rate include monitoring the volume of gas produced, the loss of mass, the change in turbidity (cloudiness), or the change in colour.

常用的速率测定方法包括监测生成气体的体积、质量的减少、浊度的变化或颜色的变化。

For example, in the reaction between marble chips and hydrochloric acid, you can collect carbon dioxide gas in a gas syringe and record its volume every 10 seconds.

例如，在大理石碎块与盐酸的反应中，你可以用注射器收集二氧化碳气体，并每 10 秒记录一次体积。

Rate = Δ(amount) / Δt

3. Collision Theory | 碰撞理论

For two particles to react, they must collide with each other with sufficient energy, called the activation energy (Eₐ), and with the correct orientation.

要使两个粒子发生反应，它们必须互相碰撞，并且具备足够的能量（称为活化能 Eₐ），同时碰撞方向要正确。

Only a tiny fraction of collisions are effective. The rate of reaction depends on how often effective collisions occur. If you increase the number of effective collisions per second, the rate increases.

只有极少数的碰撞是有效碰撞。反应速率取决于单位时间内有效碰撞发生的次数。如果每秒有效碰撞次数增加，速率就会加快。

Factors such as concentration, temperature, surface area, pressure, and catalysts all work by changing the frequency or energy of collisions.

浓度、温度、表面积、压力和催化剂等因素的作用，都是通过改变碰撞频率或碰撞能量来实现的。

4. Concentration | 浓度

Increasing the concentration of a solution means there are more reactant particles in the same volume. Therefore, the reactant particles are closer together, resulting in more frequent collisions.

增大溶液的浓度意味着在相同体积内有更多的反应物粒子。因此，反应物粒子之间的距离更小，碰撞更加频繁。

However, concentration changes usually do not change the energy of collisions. The rate simply increases because the collision frequency rises.

但是，浓度变化通常不会改变碰撞的能量。速率提高仅仅是因为碰撞频率增加了。

Graph interpretation: A higher concentration gives a steeper curve at the start and a shorter reaction time.

图像解读：浓度越高，起始曲线越陡，反应完成所需的时间越短。

5. Temperature | 温度

Heating a reaction mixture increases the average kinetic energy of the particles. The particles move faster, so they collide more often and with more energy.

加热反应混合物会增加粒子的平均动能。粒子运动得更快，因此它们碰撞的次数更多，每次碰撞的能量也更大。

A small rise in temperature can greatly increase the rate, because many more particles now have energy greater than or equal to the activation energy.

温度的小幅升高就能大幅提高反应速率，因为此时有更多的粒子能量达到或超过活化能。

As a rule of thumb, for many reactions at room temperature, a 10 °C rise roughly doubles the rate.

近似地说，对于许多室温下的反应，温度每升高 10 °C，反应速率大约翻倍。

6. Surface Area | 表面积

When a solid reactant is broken into smaller pieces, its total surface area increases. More particles are exposed to the other reactant, so there are more possible collision sites.

当固体反应物被分割成更小的碎块时，其总表面积增大。更多的粒子暴露在另一种反应物面前，因此可供碰撞的位置更多。

In reactions involving solids, a powdered solid reacts much faster than a single large lump of the same mass.

在涉及固体的反应中，相同质量的粉末状固体比一大块固体反应快得多。

Surface area ↑ → collision frequency ↑ → rate ↑

7. Catalysts | 催化剂

A catalyst is a substance that increases the rate of reaction without being used up in the overall reaction. It provides an alternative reaction pathway with a lower activation energy.

催化剂是一种能提高反应速率但在整个反应中本身不被消耗的物质。它提供了一条具有较低活化能的替代反应路径。

Because the activation energy is lower, a much larger proportion of collisions become effective. Thus, the rate increases significantly.

由于活化能降低，碰撞的有效比例大幅增加，因此反应速率显著提高。

Catalysts are important in industry because they reduce energy costs, speed up production, and can be reused. Examples include iron in the Haber process and vanadium(V) oxide in the contact process.

催化剂在工业中非常重要，因为它们能降低能源成本、加快生产，并且可以重复使用。例如哈伯法中的铁，以及接触法中的五氧化二钒。

8. Pressure (for Gases) | 压力（气体）

For reactions involving gases, increasing the pressure effectively increases the concentration of gas particles because the particles are squeezed into a smaller volume.

对于涉及气体的反应，增大压力实际上就是增大气体粒子的浓度，因为粒子被压缩到更小的体积中。

This causes more frequent collisions between gas particles, so the rate of reaction increases. Pressure does not affect reactions that involve only liquids or solids.

这会使得气体粒子之间的碰撞更加频繁，因此反应速率增大。压力只影响含有气体的反应，对仅涉及液体或固体的反应没有影响。

In the Haber process, high pressures are used to improve the rate and yield of ammonia production.

在哈伯法中，使用高压来提高氨生成的速率和产率。

9. Graphs of Reaction Rates | 反应速率图

Reaction data is often displayed as a graph of amount (volume, mass, or concentration) against time. The steeper the slope, the faster the reaction.

反应数据通常以生成量（体积、质量或浓度）对时间的图像来表示。斜率越陡，反应越快。

As reactants are used up, the graph becomes less steep and eventually becomes flat when the reaction stops (when at least one reactant is fully consumed).

随着反应物的消耗，图像逐渐变平缓，当反应停止时（至少一种反应物耗尽）曲线变成水平直线。

Feature \| 特征	Meaning \| 含义
Initial slope	Rate at the beginning
Final flat line	Reaction finished
Changing slope	Rate is changing

The total height of the curve at the end gives the total amount of product formed, which depends on the amount of limiting reactant.

曲线最终的高度表示生成产物的总量，这取决于限制反应物的量。

10. Calculating Average Rate | 计算平均速率

To calculate an average rate over a time interval, you use the formula:

要计算某段时间间隔内的平均速率，可以使用以下公式：

Average rate = (change in quantity) / (change in time)

For example, if 40 cm³ of carbon dioxide is produced in the first 20 seconds, the average rate for the first 20 s is:

例如，如果前 20 秒内生成了 40 cm³ 的二氧化碳，那么前 20 s 的平均速率为：

Rate = 40 / 20 = 2 cm³/s

The units of rate depend on what quantity is measured: g/s, cm³/s, mol/s, or another combination.

速率的单位取决于所测量的量：g/s、cm³/s、mol/s 等不同组合。

11. Applications in Industry | 工业应用

Understanding rate of reaction is essential for designing industrial processes. For example, in the production of sulfuric acid, vanadium(V) oxide is used as a catalyst to increase the rate of SO₂ to SO₃ conversion.

理解反应速率对于设计工业过程至关重要。例如，在硫酸生产中，使用五氧化二钒作为催化剂，以提高 SO₂ 转化为 SO₃ 的速率。

In food storage, lowering temperature slows down the reactions that cause food to spoil, which is why refrigerators extend the shelf life of food.

在食品储存方面，降低温度会减缓导致食品腐败的反应速率，这就是冰箱能延长食品保质期的原因。

Chemists use the principles of rate to choose optimal conditions—pressure, temperature, concentration, and catalysts—for maximum efficiency and profitability.

化学家利用速率原理来选择最佳条件——压力、温度、浓度和催化剂——以实现最高的效率和利润。

12. Summary | 总结

Rates of reaction are controlled by the frequency and effectiveness of particle collisions. Concentration, pressure, surface area, temperature, and catalysts all alter rate in predictable ways.

反应速率由粒子碰撞的频率和有效程度控制。浓度、压力、表面积、温度和催化剂都以可预测的方式改变速率。

Increasing temperature, concentration, pressure, or surface area → faster reaction
增加温度、浓度、压力或表面积 → 反应加快
Adding a catalyst → faster reaction by lowering activation energy
加入催化剂 → 通过降低活化能加快反应
Graphs and rate calculations help us quantify and compare reactivity
图像和速率计算帮助我们量化和比较反应活性

Mastering these ideas allows you to explain everyday phenomena and industrial choices with confidence.

掌握这些概念，你就能自信地解释日常现象和工业选择。

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Rates of Reaction | 反应速率