📚 Experiment 659: Effect of Temperature on Reaction Rate | 实验 659：温度对反应速率的影响
Experiment 659 is a classic IGCSE Science investigation used to examine how changing temperature affects the rate of a chemical reaction. In this experiment, sodium thiosulfate solution reacts with hydrochloric acid to produce a precipitate of sulfur, which makes the solution go cloudy. By timing how long it takes for the cross beneath the flask to disappear at different temperatures, we can calculate and compare reaction rates. This investigation provides clear evidence for the collision theory and helps students understand the kinetic particle model in a practical context.
实验 659 是 IGCSE 科学课程中一个经典的探究活动，用于研究温度变化如何影响化学反应速率。该实验让硫代硫酸钠溶液与盐酸反应，生成硫沉淀使溶液变浑浊。通过记录不同温度下锥形瓶底部十字标记消失所需的时间，我们可以计算并比较反应速率。这个实验为碰撞理论提供了清晰的证据，并帮助学生在实践中理解粒子运动模型。
1. Purpose of Experiment 659 | 实验 659 的目的
The main purpose of this experiment is to determine the effect of temperature on the rate of reaction between sodium thiosulfate and hydrochloric acid. A secondary aim is to practise measuring reaction time and calculating rate as 1/time, then plotting a graph of rate against temperature. This skill is directly assessed in Edexcel IGCSE Science practical-based questions.
本实验的主要目的是测定温度对硫代硫酸钠与盐酸反应速率的影响。次要目标是练习测量反应时间、用 1/时间 计算速率，并绘制速率-温度关系图。这一技能在 Edexcel IGCSE 科学实验类考题中直接考查。
2. Underlying Theory: Collision Theory | 基本原理：碰撞理论
Reactions occur when reacting particles collide with sufficient energy, known as the activation energy, and with the correct orientation. Increasing the temperature gives particles more kinetic energy. They move faster, so collisions become more frequent and, more importantly, a greater proportion of collisions have energy equal to or greater than the activation energy. Both factors cause the rate of reaction to increase.
当反应粒子以足够的能量（即活化能）和正确的取向发生碰撞时，反应才会发生。升高温度使粒子获得更多的动能，它们运动得更快，因此碰撞更频繁；更重要的是，更多比例碰撞的能量达到或超过活化能，这两个因素都使反应速率提高。
3. Chemical Equation and Observations | 化学方程式与观察现象
The reaction in Experiment 659 is:
Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + SO₂(g) + S(s) + H₂O(l)
实验 659 涉及的反应为：
Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + SO₂(g) + S(s) + H₂O(l)
As the reaction proceeds, solid sulfur is produced as a fine yellow precipitate. This makes the solution turn cloudy. The time taken for the cross drawn on paper underneath the conical flask to become no longer visible is used as a measure of the reaction rate.
随着反应进行，生成固态硫的细小黄色沉淀，使溶液变浑浊。锥形瓶下方纸上画的十字标记完全看不见所需的时间，被用作衡量反应速率的指标。
4. Apparatus and Chemicals | 器材与化学品
The following items are needed:
- Sodium thiosulfate solution (e.g. 0.1 mol dm⁻³)
- Hydrochloric acid (e.g. 1.0 mol dm⁻³)
- Conical flask (100 cm³ or 250 cm³)
- Measuring cylinders (10 cm³ and 50 cm³)
- Stopwatch
- Thermometer (-10 °C to 110 °C)
- Water bath and ice
- White paper with a dark cross drawn on it
- Safety goggles and lab coat
所需器材如下：
- 硫代硫酸钠溶液（如 0.1 mol dm⁻³）
- 盐酸（如 1.0 mol dm⁻³）
- 锥形瓶（100 cm³ 或 250 cm³）
- 量筒（10 cm³ 和 50 cm³）
- 秒表
- 温度计（-10 °C 至 110 °C）
- 水浴和冰块
- 画有深色十字的白纸
- 护目镜和实验服
5. Method for Experiment 659 | 实验 659 的步骤
1. Place the conical flask on the paper with the cross clearly visible from above.
2. Use a measuring cylinder to add 50 cm³ of sodium thiosulfate solution into the flask.
3. Measure and record the initial temperature of the solution.
4. If testing above room temperature, warm the flask gently in a water bath. For temperatures below room temperature, cool the solution using an ice-water bath.
5. Add 5 cm³ of hydrochloric acid, start the stopwatch immediately and swirl the flask once.
6. Look down through the solution and stop the stopwatch when the cross can no longer be seen.
7. Record the time and the temperature. Repeat for at least five different temperatures.
1. 将锥形瓶放在白纸上，确保从上方能清楚看到十字标记。
2. 用量筒量取 50 cm³ 硫代硫酸钠溶液加入锥形瓶中。
3. 测量并记录溶液的初始温度。
4. 如需测试高于室温的条件，将锥形瓶在水浴中温和加热。低于室温时，使用冰水浴冷却溶液。
5. 加入 5 cm³ 盐酸，立即启动秒表并轻轻旋转锥形瓶一次。
6. 从溶液上方垂直向下观察，当十字恰好看不见时停止秒表。
7. 记录时间和温度。至少在五个不同温度下重复实验。
6. Results Table | 实验结果表
A typical results table for Experiment 659 is shown below. The rate of reaction is calculated as 1/time (s⁻¹) and can be multiplied by 1000 for convenience.
实验 659 的典型结果表如下所示。反应速率用 1/时间 (s⁻¹) 计算，为方便可乘以 1000。
| Temperature / °C | Time for cross to disappear / s | Rate (1/time) / s⁻¹ | Rate × 1000 / s⁻¹ |
|---|---|---|---|
| 5 | 180 | 0.0056 | 5.6 |
| 15 | 90 | 0.011 | 11 |
| 25 | 45 | 0.022 | 22 |
| 35 | 22 | 0.045 | 45 |
| 45 | 11 | 0.091 | 91 |
7. Graph and Analysis | 图表与分析
Plot temperature (x-axis, °C) against rate (y-axis, s⁻¹). The graph should show a curve that rises, indicating that rate increases with temperature. The relationship is not linear: a 10 °C rise often approximately doubles the rate. This is because the fraction of particles with energy greater than the activation energy increases rapidly with temperature, as described by the Maxwell-Boltzmann distribution.
绘制温度（x 轴，°C）对速率（y 轴，s⁻¹）的曲线。图形呈上升趋势，说明速率随温度升高而升高。该关系不是线性的：温度每升高约 10 °C，反应速率通常大致加倍。这是因为能量大于活化能的粒子比例随温度快速增加，正符合麦克斯韦-玻尔兹曼分布。
8. Conclusion from Experiment 659 | 实验 659 的结论
The experiment clearly demonstrates that increasing the temperature increases the rate of reaction. The conclusion supports the collision theory: at higher temperatures, particles move faster and collide more often, and there is a higher proportion of successful collisions. This is why the cross disappears more quickly when the solution is warmer.
实验清楚地表明，升高温度会提高反应速率。这一结论支持碰撞理论：温度较高时，粒子运动更快，碰撞更频繁，同时有效碰撞的比例更高。这就是溶液温度越高十字消失越快的原因。
9. Evaluation and Sources of Error | 实验评价与误差来源
Possible sources of error in Experiment 659 include difficulty in judging exactly when the cross disappears, leading to timing inaccuracies. The same observer should view from the same height each time. The temperature may change slightly during the reaction, so a water bath can help maintain a constant temperature. Measuring cylinders should be used carefully to obtain accurate volumes. Repeating the experiment and taking an average time can improve reliability.
实验 659 可能的误差来源包括：难以准确判断十字何时完全消失，导致计时不准；每次应由同一观察者在相同高度观察。反应过程中温度可能略有变化，使用水浴有助于维持恒温。应仔细使用量筒以获取准确的体积。重复实验并取平均时间可以提高可靠性。
10. Safety Precautions | 安全注意事项
Sulfur dioxide gas is produced, which is toxic and can cause breathing difficulties. The experiment must be carried out in a well-ventilated laboratory or a fume cupboard. Wear safety goggles throughout because hydrochloric acid is corrosive. If skin contact occurs, rinse immediately with plenty of water. Handle glassware carefully to avoid breakages and cuts.
反应过程中会产生有毒的二氧化硫气体，可能引起呼吸困难。实验必须在通风良好的实验室或通风橱中进行。全程佩戴护目镜，因为盐酸具有腐蚀性。如果不慎接触皮肤，立即用大量清水冲洗。小心操作玻璃器皿，避免破碎和割伤。
11. Common Exam Questions and How to Approach Them | 常见考题与解题思路
er to mention both the frequency of collisions and the energy of collisions in your explanations. When describing a safety precaution, link it directly to a specific hazard.
IGCSE 常见考题要求描述实验、分析数据、绘制图表或用碰撞理论解释趋势。试卷中可能会给出结果表，让你计算速率或预测另一温度下的反应时间。务必使用公式 rate = 1/time，并在解释时同时提及碰撞频率和碰撞能量。描述安全措施时，要将其与具体危险直接关联。
12. Extension: How Experiment 659 Links to Other Topics | 拓展：实验 659 与其他主题的联系
The concepts explored in Experiment 659 are fundamental to understanding many IGCSE Science topics. The effect of temperature on rate is also seen in enzyme-catalysed reactions, where excessive heat can denature the enzyme. In physics, the idea that particles gain kinetic energy as temperature rises explains thermal expansion and changes of state. This practical therefore strengthens cross-disciplinary understanding across the sciences.
实验 659 探讨的概念是理解许多 IGCSE 科学主题的基础。温度对速率的影响在酶催化反应中同样可见，但过高温度会使酶变性。在物理学中，温度升高导致粒子获得动能的观点解释了热膨胀和物态变化。因此，这一实践加强了对科学各科的跨学科理解。
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