📚 Rates of Reaction | 反应速率
In chemistry, the rate of a reaction tells us how quickly reactants are turned into products. Some reactions are over in a fraction of a second, while others take years. At Key Stage 3 you need to know what affects reaction rate, how to measure it, and how to explain changes using simple particle ideas.
在化学中，反应速率告诉我们反应物转化为产物的快慢。有些反应在不到一秒内完成，有些则需要数年。在 KS3 阶段，你需要了解哪些因素会影响反应速率、如何测量反应速率，以及如何用简单的粒子观点解释变化。
1. What Is Reaction Rate? | 什么是反应速率
A chemical reaction changes reactants into products. The rate of reaction tells us how fast this change happens. Some reactions, such as burning magnesium, are very fast; others, such as iron rusting, are very slow.
化学反应把反应物变成产物。反应速率告诉我们这种变化发生得有多快。有些反应（如镁条燃烧）非常快；有些反应（如铁生锈）则非常慢。
In the laboratory you can measure rate by recording the amount of product formed or the amount of reactant used up in a certain time. We can calculate a mean rate using this equation:
在实验室中，你可以通过记录一定时间内生成产物的量或消耗反应物的量来测量反应速率。我们可以用下面的公式计算平均速率：
mean rate of reaction = amount of product formed ÷ time taken
平均反应速率 = 生成产物的量 ÷ 所用时间。速率的常用单位包括 cm³/s 或 g/s。
2. Collision Theory | 碰撞理论
Everything is made of particles. According to collision theory, particles must collide before they can react. Only collisions with enough energy can break existing bonds and start a reaction; these are called successful collisions.
万物都由粒子构成。根据碰撞理论，粒子必须先发生碰撞才能反应。只有能量足够的碰撞才能破坏已有的键并引发反应；这些碰撞称为有效碰撞。
The rate of reaction depends on how often particles collide successfully. More frequent successful collisions give a faster reaction.
反应速率取决于粒子成功碰撞的频率。成功碰撞越频繁，反应速率越快。
3. Effect of Concentration | 浓度的影响
Concentration tells us how much solute is dissolved in a certain volume of solvent. In a solution, increasing the concentration packs more reacting particles into the same space.
浓度表示在一定体积溶剂中溶解了多少溶质。在溶液中，增大浓度会使更多反应粒子挤在同一空间中。
With more particles in the same volume, collisions happen more often, so the rate of reaction increases. For example, marble chips react faster with 2 mol/dm³ hydrochloric acid than with 0.5 mol/dm³ acid.
相同体积内粒子更多，碰撞就更频繁，因此反应速率增大。例如，大理石碎片与 2 mol/dm³ 盐酸的反应比与 0.5 mol/dm³ 盐酸的反应更快。
4. Effect of Temperature | 温度的影响
Raising the temperature gives particles more kinetic energy, so they move faster. Faster particles collide more often and with more force.
升高温度使粒子获得更多动能，因此运动得更快。运动更快的粒子碰撞更频繁、更有力。
More of these collisions have enough energy to be successful. This is why food spoils faster in a warm kitchen than in a fridge.
这些碰撞中有更多具备足够的能量成为有效碰撞。这就是为什么食物在温暖的厨房里比在冰箱里变质得更快。
5. Effect of Surface Area | 表面积的影响
For solid reactants, only particles on the surface can collide with particles in the solution or gas around them. Breaking a solid into smaller pieces increases its surface area.
对于固体反应物，只有表面的粒子才能与周围溶液或气体中的粒子碰撞。把固体弄成更小的碎块可以增大表面积。
A larger surface area exposes more solid particles to collisions, so the reaction goes faster. Powdered marble reacts faster than large marble chips.
更大的表面积使更多固体粒子暴露出来参与碰撞，因此反应更快。粉末状大理石比大块大理石反应更快。
6. Catalysts | 催化剂
A catalyst is a substance that speeds up a reaction without being used up itself. It provides an alternative reaction pathway with lower energy requirements.
催化剂是一种能加快反应速率而本身不被消耗的物质。它提供了一条能量需求更低的替代反应路径。
Catalysts are not included in the overall word equation and their mass is the same at the end. Enzymes are biological catalysts that control reactions in living things.
催化剂不出现在总文字方程式中，反应结束时其质量不变。酶是控制生物体内反应的生物催化剂。
For example, manganese dioxide speeds up the breakdown of hydrogen peroxide into water and oxygen.
例如，二氧化锰能加快过氧化氢分解为水和氧气的反应。
7. Measuring Rate: Gas Production | 测量反应速率：气体产生
One common method is to collect the gas given off in a gas syringe or an inverted measuring cylinder. You record the volume of gas at regular time intervals, such as every 10 seconds.
一种常用方法是用气体注射器或倒置量筒收集生成的气体。你每隔一定时间（如每 10 秒）记录一次气体体积。
A suitable reaction is calcium carbonate (marble chips) with hydrochloric acid. This produces carbon dioxide gas, water and calcium chloride.
一个适合的反应是碳酸钙（大理石碎片）与盐酸反应。该反应生成二氧化碳气体、水和氯化钙。
You can then plot volume of gas against time to compare rates under different conditions.
然后你可以绘制气体体积随时间变化的图像，以比较不同条件下的反应速率。
8. Measuring Rate: Mass Loss and Turbidity | 测量反应速率：质量减少和浑浊
If a gas escapes from an open flask, the total mass of the reaction mixture decreases. You can place the flask on a balance and record the mass at regular intervals.
如果气体从敞口烧瓶中逸出，反应混合物的总质量会减少。你可以把烧瓶放在天平上，每隔一段时间记录一次质量。
Another method is used when a precipitate forms. For example, sodium thiosulfate solution reacts with hydrochloric acid to make a pale yellow sulfur precipitate, which turns the mixture cloudy.
另一种方法用于生成沉淀的反应。例如，硫代硫酸钠溶液与盐酸反应生成淡黄色硫沉淀，使混合物变浑浊。
You can measure the time taken for a cross drawn under the flask to disappear. A faster reaction makes the cross disappear in a shorter time.
你可以测量烧瓶下方画的十字消失所需的时间。反应越快，十字消失所需时间越短。
9. Interpreting Rate Graphs | 解读速率图
A rate graph usually shows the amount of product formed or reactant used on the vertical axis and time on the horizontal axis.
速率图通常在纵轴表示生成产物或消耗反应物的量，在横轴表示时间。
A steep line means a fast reaction because a lot of product is made in a short time. A shallow line means a slow reaction.
陡峭的曲线表示反应快，因为在短时间内生成了大量产物。平缓的曲线表示反应慢。
When the line becomes flat, the reaction has stopped. The limiting reactant has been used up.
当曲线变平时，反应已经停止。限制反应物已经耗尽。
If you compare two lines on the same axes, the steeper line shows the faster rate, which may be caused by higher concentration, higher temperature, larger surface area or a catalyst.
如果在同一坐标轴上比较两条曲线，较陡的一条表示速率更快，这可能是由更高的浓度、更高的温度、更大的表面积或催化剂引起的。
10. Summary and Exam Tips | 总结与考试技巧
The key factors that increase reaction rate are higher concentration, higher temperature, larger surface area and the use of a catalyst. All of these increase the frequency of successful collisions between reacting particles.
提高反应速率的关键因素包括：增大浓度、升高温度、增大表面积以及使用催化剂。所有这些因素都会增加反应粒子之间有效碰撞的频率。
In an experiment, change only one factor at a time and keep all other variables the same, so the test is fair. This is called a controlled investigation.
在实验中，每次只改变一个因素，并保持其他所有变量相同，这样实验才公平。这称为控制变量探究。
Always quote units when calculating a rate, for example cm³/s or g/s. Use a ruler to compare slopes on a graph and refer to collision theory in explanation questions.
计算速率时一定要写明单位，例如 cm³/s 或 g/s。在图像题中用直尺比较斜率，在解释题中要联系碰撞理论。
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