📚 5 Catalysts and Reaction Rate | 催化剂与反应速率
Reactions happen at different speeds. Some, like explosions, are over in a fraction of a second. Others, like rusting, can take years. In KS3 chemistry, we learn how to measure and change reaction rates. This unit focuses on catalysts and the factors that speed up or slow down chemical reactions. You will discover why catalysts are useful, how they work, and why they matter in industry and living things.
化学反应发生的速度各不相同。有些反应（如爆炸）在不到一秒内完成；有些反应（如铁生锈）则需要数年时间。在 KS3 化学中，我们学习如何测量和改变反应速率。本单元重点介绍催化剂以及加快或减慢化学反应的因素。你将了解催化剂为什么有用、它们如何工作，以及它们为什么在工业和生物体内都很重要。
1. What is Reaction Rate? | 什么是反应速率
The reaction rate tells us how quickly reactants are used up or products are made. If a reaction is fast, the products appear quickly. If it is slow, the change takes a long time.
反应速率告诉我们反应物被消耗或产物生成的速度有多快。如果反应快，产物就会很快出现；如果反应慢，变化就需要很长时间。
We can measure rate by recording the volume of gas produced over time, or by timing how long a solid takes to disappear. The unit for rate could be cm³/s if we measure gas volume.
我们可以通过记录一段时间内产生的气体体积，或记录固体消失所需的时间来测量速率。如果测量气体体积，速率的单位可以是 cm³/s。
2. Collision Theory | 碰撞理论
For a reaction to happen, particles must collide with enough energy. This idea is called collision theory. Not every collision causes a reaction. Particles must also be pointing the right way.
反应要发生，微粒必须碰撞并且具有足够的能量。这个观点叫做碰撞理论。并非每次碰撞都会引发反应；微粒还必须朝向正确的方向。
The minimum energy needed for a successful collision is called activation energy. If particles collide with less energy than this, they simply bounce apart.
成功碰撞所需的最低能量叫做活化能。如果微粒碰撞时的能量低于活化能，它们就会弹开。
Anything that increases the number of successful collisions per second will increase the reaction rate.
任何增加每秒成功碰撞次数的方法都会提高反应速率。
3. Temperature and Rate | 温度与速率
Heating a reaction mixture gives particles more kinetic energy. They move faster and collide more often. More importantly, a larger fraction of collisions now have enough energy to overcome the activation energy barrier.
加热反应混合物会使微粒获得更多动能。它们运动更快，碰撞更频繁。更重要的是，现在有更大比例的碰撞具有足够能量来克服活化能屏障。
This is why food cooks faster in a hot oven, and why magnesium ribbon reacts much faster with hot acid than with cold acid.
这就是为什么食物在热烤箱中熟得更快，也是为什么镁条与热酸的反应比与冷酸的反应快得多。
4. Concentration and Rate | 浓度与速率
If a solution is more concentrated, there are more reactant particles in the same volume. This means collisions happen more often, so the rate increases. For gases, increasing pressure has a similar effect because the particles are squeezed closer together.
如果溶液浓度更高，相同体积内反应物微粒就更多。这意味着碰撞更频繁，因此速率增加。对于气体，增大压强有类似效果，因为微粒被压得更近。
For example, magnesium reacts faster with 2 mol/dm³ hydrochloric acid than with 0.5 mol/dm³ acid, because the acid particles are closer together.
例如，镁与 2 mol/dm³ 盐酸的反应比与 0.5 mol/dm³ 盐酸更快，因为酸微粒更密集。
5. Surface Area and Rate | 表面积与速率
Breaking a solid into smaller pieces increases its surface area. More particles are exposed and available to collide, so the reaction speeds up. Dust and powders can react extremely quickly because they have a huge surface area.
把固体分成小块会增加其表面积。更多微粒暴露出来并可以参与碰撞，因此反应加快。粉尘和粉末反应极快，因为它们的表面积非常大。
A large lump of calcium carbonate fizzes gently in acid, but the same mass as powder fizzes violently.
一大块碳酸钙在酸中会轻轻冒泡，但相同质量的粉末则会剧烈冒泡。
6. What is a Catalyst? | 什么是催化剂
A catalyst is a substance that speeds up a chemical reaction without being used up itself. At the end of the reaction, the catalyst is still there, unchanged in mass and chemical properties.
催化剂是一种能加快化学反应但本身不被消耗的物质。反应结束后，催化剂仍然存在，质量和化学性质不变。
Catalysts are not reactants. They do not appear in the overall word equation, but they take part in the reaction and are regenerated.
催化剂不是反应物。它们不出现在总文字方程式中，但它们参与反应并在反应过程中再生。
A catalyst lowers the activation energy by providing an alternative reaction pathway. This means more particles have enough energy to react, so the rate increases without raising the temperature.
催化剂通过提供另一条反应途径来降低活化能。这意味着更多微粒具有足够能量发生反应，因此无需升高温度就能提高速率。
7. How Catalysts Work | 催化剂如何工作
Many catalysts work by adsorption. Reactant molecules stick to the surface of the catalyst. This weakens their bonds and holds them in the right position. The reactants then react more easily, and the products leave the surface.
许多催化剂通过吸附起作用。反应物分子附着在催化剂表面。这会削弱它们的化学键并使它们保持在正确位置。反应物因此更容易反应，产物随后离开催化剂表面。
A common example is the decomposition of hydrogen peroxide. Hydrogen peroxide solution breaks down very slowly on its own. Adding a small amount of manganese(IV) oxide makes oxygen gas bubble out rapidly. The black powder can be filtered off and used again.
一个常见例子是过氧化氢分解。过氧化氢溶液本身分解非常缓慢。加入少量二氧化锰会使氧气迅速冒出。黑色的二氧化锰粉末可以过滤出来再次使用。
hydrogen peroxide → water + oxygen
With manganese(IV) oxide as the catalyst, we write the catalyst above the arrow.
二氧化锰作为催化剂，写在箭头上面。
8. Catalysts in Everyday Life | 日常生活中的催化剂
Catalysts are used in industry to make products faster and at lower temperatures, saving energy and money. The Haber process uses an iron catalyst to make ammonia. Catalytic converters in cars contain platinum and rhodium. They convert harmful gases like carbon monoxide and nitrogen oxides into less harmful carbon dioxide and nitrogen.
催化剂在工业中用于在较低温度下更快地制造产品，从而节省能源和成本。哈伯法使用铁催化剂制造氨。汽车催化转化器含有铂和铑。它们将一氧化碳和氮氧化物等有害气体转化为危害较小的二氧化碳和氮气。
Without catalysts, many important reactions would be too slow to be useful. Catalysts allow companies to use lower temperatures, which reduces fuel bills.
没有催化剂，许多重要反应会慢得无法使用。催化剂使企业能够使用较低温度，从而降低燃料费用。
9. Enzymes: Biological Catalysts | 酶：生物催化剂
Living things use special catalysts called enzymes. Enzymes are proteins that speed up reactions in cells, such as breaking down food or building new molecules. Each enzyme is specific to one type of reaction.
生物体使用称为酶的特殊催化剂。酶是蛋白质，能加速细胞内的反应，例如分解食物或构建新分子。每种酶只对一种类型的反应具有特异性。
Catalase is an enzyme found in many cells. It breaks down hydrogen peroxide into water and oxygen very quickly, protecting cells from damage. This is why raw potato speeds up the decomposition of hydrogen peroxide in the lab.
过氧化氢酶是许多细胞中存在的一种酶。它能非常迅速地将过氧化氢分解为水和氧气，保护细胞免受伤害。这就是为什么生土豆在实验室中能加快过氧化氢分解的原因。
Enzymes work best at specific temperatures and pH values. Very high temperatures denature the enzyme, changing the shape of its active site so the substrate no longer fits.
酶在特定温度和 pH 值下活性最高。高温会使酶变性，改变其活性位点的形状，使底物不再契合。
10. Catalysts and Activation Energy | 催化剂与活化能
The key effect of a catalyst is to lower the activation energy, often written as Eₐ. Imagine activation energy as a hill that reactant particles must climb before they can roll down to form products. A catalyst makes the hill lower. More particles can get over it, so the rate increases.
催化剂的关键作用是降低活化能，通常写作 Eₐ。可以把活化能想象成反应物微粒在形成产物之前必须爬过的山丘。催化剂使山丘变低。更多微粒能够越过它，因此速率增加。
It is important to understand that a catalyst does not change the energy of the reactants or products. It only lowers the energy barrier between them. The overall energy change, ΔH, stays exactly the same.
重要的是要理解，催化剂不会改变反应物或产物的能量。它只降低两者之间的能量屏障。总能量变化 ΔH 保持完全相同。
This explains why catalysts are so powerful: a small amount can transform a reaction from extremely slow to rapid, without being consumed.
这解释了催化剂为何如此强大：少量催化剂就能使反应从极慢变为快速，而本身不被消耗。
11. Investigating Reaction Rates | 探究反应速率
In the laboratory, you might investigate how a catalyst affects the rate of hydrogen peroxide decomposition. A simple method is to place hydrogen peroxide solution in a conical flask, add a small amount of manganese(IV) oxide, and quickly attach a gas syringe or an upturned measuring cylinder to collect oxygen gas.
在实验室中，你可以探究催化剂如何影响过氧化氢分解速率。一个简单的方法是：将过氧化氢溶液放入锥形瓶中，加入少量二氧化锰，迅速连接气体注射器或倒置量筒收集氧气。
Record the volume of oxygen produced every 10 seconds. Plot a graph of gas volume against time. The steeper the line, the faster the reaction. When the line flattens, the reaction has finished.
每 10 秒记录一次产生的氧气体积。绘制气体体积随时间变化的图像。曲线越陡，反应越快。当曲线趋于平缓时，反应结束。
A control experiment without the catalyst should produce very little gas over the same time. Comparing the gradients of the two graphs shows how much the catalyst speeds up the reaction.
不加催化剂的对照实验在相同时间内应当几乎不产生气体。比较两条曲线的斜率可以显示催化剂使反应加快了多少。
12. Why Catalysts Matter | 催化剂为何重要
Catalysts help make chemistry more sustainable. They allow reactions to happen at lower temperatures and pressures, which saves energy. They also reduce waste because they are not used up and can be reused many times.
催化剂有助于使化学更可持续。它们使反应能在较低温度和压力下发生，从而节省能源。它们还减少浪费，因为它们不被消耗并且可以多次重复使用。
From the enzymes inside your body to the catalytic converter in a car, catalysts are essential to both life and modern technology. Understanding them helps us design faster, cheaper, and greener chemical processes.
从体内的酶到汽车中的催化转化器，催化剂对生命和现代技术都至关重要。了解催化剂有助于我们设计更快、更便宜、更环保的化学过程。
Always remember the key rule: a catalyst changes the speed of a reaction but remains chemically unchanged at the end.
永远记住关键规则：催化剂改变反应的速率，但反应结束时化学性质保持不变。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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