📚 768: Investigating How Temperature Affects Rate of Reaction | 768: 探究温度如何影响反应速率
This core practical focuses on measuring the effect of temperature on the rate of the reaction between sodium thiosulfate and hydrochloric acid. The experiment is a key part of the Edexcel IGCSE Science (Double Award) specification and helps students develop skills in controlling variables, recording time-based data and evaluating the reliability of results.
本核心实验旨在探究温度对硫代硫酸钠与盐酸反应速率的影响。该实验是Edexcel IGCSE科学（双奖）课程的重要环节，能够帮助学生掌握控制变量、记录基于时间的数据以及评估结果可靠性的技能。
1. Context and Syllabus Links | 背景与考纲衔接
The reaction produces a yellow precipitate of sulfur, which turns the solution opaque. By measuring the time taken for a cross drawn on paper to 'disappear' when viewed through the reaction mixture, you can calculate an approximate rate for the reaction. This practical is explicitly listed in the Edexcel IGCSE Chemistry (4CH1) and Science (4SD0) specifications under 'Rates of reaction and energy changes'.
该反应生成黄色的硫沉淀，使溶液变得浑浊。通过测量反应混合物遮盖纸上所画十字所需的时间，可以计算出近似的反应速率。该实验明确出现在Edexcel IGCSE化学（4CH1）和科学（4SD0）考纲“反应速率与能量变化”专题中。
Temperature is one of the four key factors affecting reaction rate, alongside concentration, surface area and the use of a catalyst. Mastery of this investigation provides evidence for the particle collision theory and is regularly assessed in both paper-based and practical examinations.
温度是影响反应速率的四大关键因素之一，另外三个因素为浓度、表面积和使用催化剂。掌握该实验可为粒子碰撞理论提供证据，并经常在笔试和实验考试中被考查。
2. Scientific Principle | 科学原理
l). The fine yellow sulfur particles scatter light, causing the solution to become cloudy.
反应为：硫代硫酸钠 + 盐酸 → 硫 + 二氧化硫 + 氯化钠 + 水。用符号表示为：Na₂S₂O₃(aq) + 2HCl(aq) → S(s) + SO₂(g) + 2NaCl(aq) + H₂O(l)。生成的细小黄色硫颗粒会散射光线，使溶液变浑浊。
Increasing temperature gives reactant particles more kinetic energy. This leads to more frequent collisions and, more importantly, a greater proportion of collisions have energy equal to or greater than the activation energy. Both effects cause the rate to rise sharply with temperature.
升高温度赋予反应物粒子更多的动能。这导致碰撞更加频繁，且更重要的是，更高比例的碰撞具有大于或等于活化能的能量。这两种效应使反应速率随温度急剧上升。
3. Apparatus and Chemicals | 仪器与药品
- 100 cm³ measuring cylinder – to measure sodium thiosulfate solution / 100 cm³量筒——用于量取硫代硫酸钠溶液
- 10 cm³ measuring cylinder – for hydrochloric acid / 10 cm³量筒——用于量取盐酸
- 250 cm³ conical flask / 250 cm³锥形瓶
- Piece of white paper with a dark cross drawn on it / 一张画有深色十字的白纸
- Stopwatch or timer / 停表或计时器
- Thermometer (0–100°C) / 温度计（0–100°C）
- Water bath or large beaker for heating / 水浴或大烧杯用于加热
- 0.1 mol/dm³ sodium thiosulfate solution, Na₂S₂O₃ / 0.1 mol/dm³硫代硫酸钠溶液
- 2 mol/dm³ hydrochloric acid, HCl (irritant) / 2 mol/dm³盐酸（刺激性）
- Safety goggles and lab coat / 护目镜和实验服
4. Safety Precautions | 安全措施
Wear safety goggles at all times. Hydrochloric acid is an irritant and should be handled with care. Sulfur dioxide gas is produced, which is toxic and can trigger asthma attacks; carry out the experiment in a well-ventilated laboratory or use a fume cupboard if required by your school's risk assessment. Hot water and heated solutions present a burn hazard; allow apparatus to cool before handling.
全程佩戴护目镜。盐酸具有刺激性，应小心处理。反应会生成有毒的二氧化硫气体，可能诱发哮喘；请在通风良好的实验室中进行实验，或根据学校的风险评估使用通风橱。热水及加热后的溶液有烫伤危险，请在操作前冷却器材。
Immediately wipe up any spills and wash hands after the practical. The sulfur precipitate should be disposed of into a filter paper and placed in chemical waste, not poured down the sink.
如有溢出请立即擦拭，实验后洗手。硫沉淀应通过滤纸收集并弃置于化学废弃物容器中，切勿倒入水槽。
5. Variables | 变量
Independent variable (what you change): temperature of the reaction mixture. This is varied by heating the sodium thiosulfate solution to approximately 20°C, 30°C, 40°C, 50°C and 60°C before adding acid. / 自变量（你改变的变量）：反应混合物的温度。通过在加入酸之前将硫代硫酸钠溶液加热至约20°C、30°C、40°C、50°C和60°C来改变。
Dependent variable (what you measure): the time taken for the cross to become no longer visible. This is used to calculate the relative rate of reaction as 1/time. / 因变量（你测量的变量）：十字变得不可见所需的时间。用1/时间来计算相对反应速率。
Control variables (what you keep the same): volume and concentration of sodium thiosulfate (e.g., 50 cm³ of 0.1 mol/dm³), volume and concentration of hydrochloric acid (e.g., 5 cm³ of 2 mol/dm³), size and shape of the conical flask, and the same cross drawn on white paper. / 控制变量（你保持不变的变量）：硫代硫酸钠的体积和浓度（例如50 cm³ 0.1 mol/dm³），盐酸的体积和浓度（例如5 cm³ 2 mol/dm³），锥形瓶的大小和形状，以及白纸上绘制的相同十字。
6. Method | 实验步骤
Step 1: Place the paper with the cross underneath a clean 250 cm³ conical flask. / 步骤1：将画有十字的纸垫在洁净的250 cm³锥形瓶下方。
Step 2: Using a measuring cylinder, transfer 50 cm³ of 0.1 mol/dm³ sodium thiosulfate solution into the flask. Measure the initial temperature of the solution with a thermometer and record it. If aiming for a specific temperature above room temperature, warm the thiosulfate solution gently in a water bath and check the temperature inside the flask before proceeding. / 步骤2：用量筒量取50 cm³ 0.1 mol/dm³硫代硫酸钠溶液，转移至锥形瓶中。用温度计测量溶液初始温度并记录。若需达到高于室温的特定温度，可在水浴中温和加热硫代硫酸钠溶液，并在进行下一步前检查瓶内温度。
Step 3: Measure 5 cm³ of 2 mol/dm³ hydrochloric acid in a small measuring cylinder. / 步骤3：用小量筒量取5 cm³ 2 mol/dm³盐酸。
Step 4: Add the acid to the flask and immediately start the stopwatch. Swirl the flask once to mix the reactants. / 步骤4：将酸加入锥形瓶中并立即启动停表。轻轻旋摇锥形瓶一次以混合反应物。
Step 5: Observe the cross from directly above the flask. Stop the stopwatch as soon as the cross can no longer be seen. Record the time and the final temperature (the mean of initial and final temperature gives a more accurate reaction temperature). / 步骤5：从锥形瓶正上方观察十字。一旦十字不再可见即停止计时。记录时间和最终温度（初始温度和最终温度的平均值可给出更准确的反应温度）。
Step 6: Repeat the experiment at four other temperatures, between approximately 20°C and 60°C. At least two readings should be taken at each temperature to allow calculation of a mean. / 步骤6：在约20°C至60°C的另外四个温度下重复实验。每个温度至少获取两次读数以计算平均值。
7. Recording Results | 记录结果
Design a suitable results table. It should have columns for temperature (initial and final or average), time taken for the cross to disappear (trial 1, trial 2, mean) and the calculated rate (1/mean time). An example layout is shown below:
设计一个合适的实验结果表。表格应包括温度（初始和最终或平均温度）、十字消失所需时间（第一次试验、第二次试验、平均值）以及计算得到的速率（1/平均时间）等列。示例如下：
| Average temperature / °C 平均温度 / °C | Time 1 / s 时间1 / 秒 | Time 2 / s 时间2 / 秒 | Mean time / s 平均时间 / 秒 | Relative rate (1/t) / s⁻¹ 相对速率 (1/t) / 秒⁻¹ |
|---|---|---|---|---|
| 21 | 185 | 191 | 188 | 0.0053 |
| 30 | 92 | 88 | 90 | 0.0111 |
| 40 | 41 | 45 | 43 | 0.0233 |
| 50 | 21 | 19 | 20 | 0.0500 |
| 58 | 11 | 12 | 11.5 | 0.0870 |
Calculating the relative rate as 1/time gives a quantity that is directly proportional to the actual rate of reaction, allowing you to plot a meaningful graph. / 用1/时间计算相对速率，所得值与实际反应速率成正比，便于绘制有意义的图表。
8. Processing Data and Graphs | 数据处理与作图
Plot a graph of relative rate (on the y-axis) against average temperature (on the x-axis). Use a smooth curve of best fit through the points. The graph shows a characteristic exponential increase: a small temperature rise at low temperatures produces a significant increase in rate, but the curve continues to steepen.
绘制相对速率（y轴）随平均温度（x轴）变化的图表。通过数据点绘制一条平滑的最佳拟合曲线。该图呈典型的指数增长：低温时小幅升温可使速率显著增加，且曲线持续变得更加陡峭。
For a more linear relationship, you can also plot log(relative rate) against 1/temperature (Arrhenius approach), but at IGCSE level the simple rate–temperature graph is sufficient. In your conclusion, state clearly that increasing temperature increases the rate of reaction and explain this using particle collision theory.
为了获得更线性的关系，也可绘制log(相对速率)对1/温度的图（阿伦尼乌斯方法），但在IGCSE阶段，简单的速率–温度图即可。在结论中明确指出升高温度会加快反应速率，并运用粒子碰撞理论加以解释。
9. Typical Results and Analysis | 典型结果与分析
The results demonstrate that as the temperature increases, the time for the cross to disappear decreases sharply, meaning the rate of reaction increases. For example, at 21°C the reaction takes around 188 seconds, whereas at 58°C it takes only about 11.5 seconds. The relative rate roughly doubles with every 10°C rise, consistent with the rule of thumb for many reactions.
结果表明，随着温度升高，十字消失的时间急剧缩短，即反应速率增大。例如在21°C时反应约需188秒，而在58°C仅需约11.5秒。相对速率大约每升高10°C翻一番，这与许多反应的粗略经验法则一致。
From particle theory: at higher temperatures, particles move faster and a much larger fraction of collisions have energy equal to or exceeding the activation energy, so a higher proportion of collisions lead to product formation. This explains the non-linear relationship.
从粒子理论来看：温度较高时粒子运动更快，且具有等于或超过活化能的碰撞比例大大增加，因此发生有效碰撞并生成产物的比例更高。这解释了非线性的关系。
10. Conclusion and Evaluation | 结论与评估
Conclusion: Increasing the temperature significantly increases the rate of reaction between sodium thiosulfate and hydrochloric acid, evidenced by the decrease in time for the sulfur precipitate to obscure the cross. / 结论：升高温度显著增大了硫代硫酸钠与盐酸的反应速率，其证据是硫沉淀遮盖十字所需的时间缩短。
Evaluation of method: The experiment is simple and uses readily available chemicals. However, it relies on subjective judgement of when the cross 'disappears'. Different observers may stop the stopwatch at slightly different levels of cloudiness. To improve accuracy, use a light sensor linked to data-logging equipment to measure the transmittance of light and determine a consistent end-point. / 方法评价：实验简单且使用易得的化学品。但它依赖对十字何时“消失”的主观判断。不同的观察者可能在稍微不同的浑浊度停止计时。为提高准确性，可使用连接数据记录系统的光传感器测量透光率，从而确定一致的终点。
Additional improvements include: ensure thorough mixing by stirring the flask after adding acid (but this then becomes a variable), use a thermostatically controlled water bath to maintain temperature, and read the thermometer at eye level to avoid parallax error. Reproducibility can be checked by having other groups perform the same experiment and comparing mean times.
其他改进包括：加入酸后搅拌锥形瓶以保证充分混合（但这会引入新变量），使用恒温水浴维持温度，以及读数时保持视线水平以避免视差。可通过让其他小组重复相同实验并比较平均时间来检验可重现性。
Systematic errors: the thermometer may be uncalibrated, and the stopwatch reaction time delays are small but systematic. Random errors: slight variations in the size of the cross drawn, variation in ambient light making the end-point judgement less consistent.
系统误差：温度计可能未校准，停表反应时延虽小但属系统误差。随机误差：所画十字大小略有不同，环境光照的变化使得终点判断的一致性下降。
11. Common Exam Questions | 常见考题
Q1: Why is it unnecessary to measure the exact amount of sulfur produced? / A: Because the rate is determined by the time to reach a fixed cloudiness, which is proportional to a fixed amount of sulfur. Using 1/time gives a valid relative rate without quantifying mass.
问题1：为何没必要测量生成的硫的精确质量？ / 答：因为速率由达到固定浑浊度所需的时间决定，这与固定量的硫成正比。使用1/时间作为相对速率无需定量质量即有效。
Q2: Explain why the reaction rate increases with temperature in terms of collisions. / A: Particles gain kinetic energy, move faster, collide more often, and more collisions possess the minimum activation energy required to react.
问题2：从碰撞角度解释为何反应速率随温度升高而增加。 / 答：粒子动能增加，运动更快，碰撞更频繁，且更多碰撞具有反应所需的最低活化能。
Q3: Suggest why the same mass and concentration of reactants were used each time. / A: To keep the number of reactant particles constant, ensuring a fair test in which temperature is the only independent variable.
问题3：解释为何每次使用相同质量和浓度的反应物。 / 答：保持反应物粒子数量不变，确保公平测试，即温度是唯一的自变量。
Q4: A student obtained an anomalous time of 150 s at 50°C but 20 s at 40°C. What might have happened? / A: Possible causes include misreading the stopwatch, not mixing the reactants, using a dirty flask that contained a catalyst, or the temperature being incorrectly recorded.
问题4：某学生在50°C测得异常时间150秒，但在40°C为20秒。可能发生了什么？ / 答：可能原因包括计时器读数错误、未混合反应物、使用了含有催化剂的脏瓶，或温度记录不正确。
12. Key Takeaways | 核心要点
- Temperature is a major factor affecting reaction rate; even small increases cause large rate changes. / 温度是影响反应速率的主要因素；即使小幅升温也可导致速率巨大变化。
- The 'disappearing cross' method measures relative rate (1/time) without needing to measure concentration changes directly. / “消失的十字”法通过1/时间测量相对速率，无需直接测量浓度变化。
- ation energy; higher temperature increases the proportion of such successful collisions. / 粒子碰撞能量须≥活化能；升高温度可增大此类有效碰撞的比例。
- Control all variables carefully: volumes, concentrations, flask size and cross appearance. / 严格控制所有变量：体积、浓度、烧瓶大小和十字外观。
- Evaluate limitations: subjective endpoint, temperature loss, and potential gas hazards. Propose specific improvements. / 评价局限性：主观终点、温度损失以及潜在气体危害。提出具体改进意见。
- The relationship between temperature and rate is exponential, not linear; plotting 1/time vs temperature yields a steepening curve. / 温度与速率之间的关系是指数关系，而非线性关系；绘制1/时间对温度图得到一条逐渐变陡的曲线。
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