Rates of Reaction | 反应速率

📚 Rates of Reaction | 反应速率

Chemical reactions occur at different speeds. Understanding reaction rates is essential for controlling processes in industry, biology, and everyday life.

化学反应以不同的速度进行。理解反应速率对于控制工业、生物学及日常生活中的过程至关重要。

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1. What Is Reaction Rate? | 什么是反应速率？

The reaction rate is the change in concentration of a reactant or product per unit time. It tells us how quickly reactants are used up or products are formed.

反应速率是指反应物或生成物浓度在单位时间内的变化量。它告诉我们需要多长时间消耗完反应物或生成产物。

rate = (change in concentration) ÷ (time taken)

速率 =（浓度变化）÷（所用时间）

For example, if 2 mol/dm³ of a reactant is consumed in 10 seconds, the average rate is 0.2 mol/dm³/s.

例如，如果 2 mol/dm³ 的反应物在 10 秒内被消耗，则平均速率为 0.2 mol/dm³/s。

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2. Measuring Reaction Rates | 测量反应速率

There are several ways to measure how fast a reaction proceeds. Common methods include monitoring gas volume, mass loss, and colour change.

测量反应进行得快慢有多种方法。常见的方法包括监测气体体积、质量损失和颜色变化。

• Collecting gas in a gas syringe and recording the volume at regular time intervals.

  使用气体注射器收集气体，并每隔一定时间记录体积。

• Measuring the decrease in mass as a gas escapes from an open flask.

  测量气体从敞口烧瓶中逸出时质量的减少。

• Using a colorimeter to track changes in colour intensity for reactions involving coloured species.

  使用比色计跟踪涉及有色物质的反应中颜色强度的变化。

• Timing how long it takes for a precipitate to obscure a cross drawn on paper below the flask.

  记录沉淀使烧瓶下方纸上的十字记号变得模糊所需的时间。

The choice of method depends on the reaction type and the physical state of the substances involved.

方法的选择取决于反应类型以及所涉及物质的物理状态。

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3. Collision Theory | 碰撞理论

For a reaction to happen, particles must collide with sufficient energy (greater than or equal to the activation energy) and with the correct orientation.

要使反应发生，粒子必须携带足够的能量（大于或等于活化能）并具有正确的取向进行碰撞。

Effective collision → reaction | 有效碰撞 → 反应

Not all collisions lead to reaction. Only a small fraction are successful. Increasing the frequency of successful collisions raises the reaction rate.

并非所有碰撞都能引发反应，只有一小部分是成功的。增加有效碰撞的频率会提高反应速率。

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4. Effect of Concentration | 浓度的影响

Higher concentration means more particles per unit volume, so collisions between reactant particles become more frequent.

浓度越高，单位体积内的粒子数越多，因此反应物粒子之间的碰撞更加频繁。

For solutions, increasing concentration usually increases the rate of reaction. For gases, increasing concentration is achieved by increasing pressure.

对于溶液，增加浓度通常会加快反应速率。对于气体，增加浓度可通过增大气压来实现。

[A] ↑ → more collisions → rate ↑

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5. Effect of Pressure | 气压的影响

When the pressure of a gas is increased, the gas particles are forced closer together. This raises their concentration and therefore increases the collision frequency.

当气体压力升高时，气体粒子被压得更近。这提高了它们的浓度，从而增加碰撞频率。

Pressure changes only affect reactions involving gases. The rate increases when pressure is increased, provided the temperature remains constant.

压力变化只影响涉及气体的反应。在温度不变的情况下，增大压力会加快反应速率。

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6. Effect of Surface Area | 表面积的影响

For solids, only particles on the surface are available for collision with other reactants. Increasing the surface area of a solid by breaking it into smaller pieces exposes more particles.

对于固体，只有表面上的粒子能与其它反应物碰撞。将固体粉碎成小块以增大表面积，可以暴露更多的粒子。

More exposed particles → more frequent collisions → faster reaction. Powdered reactants react much faster than lumps.

更多暴露的粒子 → 更频繁的碰撞 → 更快的反应。粉末状反应物比块状反应物快得多。

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7. Effect of Temperature | 温度的影响

Increasing temperature makes particles move faster and have more kinetic energy. This leads to more frequent collisions and, most importantly, a greater proportion of collisions that exceed the activation energy.

升高温度使粒子运动更快并具有更大的动能。这导致碰撞更频繁，更重要的是，超过活化能的碰撞比例会增大。

Temperature ↑ → kinetic energy ↑ → successful collisions ↑

A rough rule: a 10 °C rise in temperature can double the rate of many reactions.

粗略规律：温度每升高 10 °C，许多反应的速率可以翻倍。

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8. Catalysts | 催化剂

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

催化剂是一种能提高反应速率而自身不被消耗的物质。它提供了活化能更低的不同反应途径。

With a lower activation energy, more particles have enough energy to react at the same temperature. Catalysts are specific to particular reactions.

由于活化能降低，在相同温度下更多粒子具有足够的能量发生反应。催化剂具有专一性。

Without catalyst	With catalyst
High activation energy	Lower activation energy
Slow reaction at room temperature	Fast reaction at room temperature

Enzymes are biological catalysts. In industry, transition metals are often used as catalysts, such as iron in the Haber process.

酶是生物催化剂。在工业中，过渡金属常被用作催化剂，例如哈伯法中的铁。

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9. Reaction Rate Graphs | 反应速率图

When we plot the volume of gas produced (or concentration of product) against time, we get a curve that starts steep and gradually levels off as the reactant is used up.

当我们以产生气体的体积（或生成物的浓度）对时间作图时，得到的曲线起始较陡，随后随着反应物被消耗而逐渐平缓。

The steeper the slope at a given time, the faster the reaction at that moment. The gradient can be measured by drawing a tangent to the curve.

某一时刻的斜率越陡，表示此刻反应越快。可以通过画曲线的切线来测量梯度。

If a catalyst or higher temperature is used, the initial gradient is steeper, but the final amount of product remains the same (assuming unlimited reactants).

如果使用催化剂或更高的温度，初始梯度会更陡，但最终产物的量保持不变（假设反应物足量）。

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10. Calculating Average Rate | 计算平均速率

From a graph, the average rate over a time interval can be calculated using:

从图中可以计算一段时间内的平均速率：

average rate = (change in product or reactant) ÷ (change in time)

平均速率 =（生成物或反应物的变化量）÷（时间变化量）

For example, if 40 cm³ of gas is collected in the first 20 s, the average rate is 2 cm³/s.

例如，如果前 20 秒内收集了 40 cm³ 气体，则平均速率为 2 cm³/s。

Instantaneous rate at a specific time is found from the gradient of the tangent on a concentration–time graph.

某一时刻的瞬时速率可通过浓度–时间图像上切线的斜率求得。

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11. Factors That Affect Rate – Summary | 影响速率的因素 – 总结

Factor	Effect on rate	Reason
Concentration ↑	Increases	More particles per unit volume, more collisions
Pressure ↑ (gases)	Increases	Gas particles closer, more collisions
Surface area ↑	Increases	More exposed particles available to collide
Temperature ↑	Increases	More kinetic energy, more successful collisions
Catalyst added	Increases	Provides lower activation energy pathway

Memory aid: concentration, pressure, surface area, temperature, and catalyst – these five factors control how fast reactions go.

记忆口诀：浓度、压力、表面积、温度、催化剂 – 这五个因素控制反应进行的快慢。

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