📚 Year 7 AQA Chemistry: In-Depth Past Paper Analysis | 七年级AQA化学：历年真题深度解析
In Year 7 AQA Science, the chemistry component introduces fundamental concepts that lay the groundwork for future GCSE success. This article provides a deep dive into common past paper questions, revealing the key patterns, examiner expectations, and common pitfalls. By analysing actual exam-style problems on states of matter, atoms, elements, compounds, reactions, acids and alkalis, we will strengthen your understanding and exam technique. Each section dissects a classic question, explains the best approach, and gives you the model answer logic you need to improve your marks.
在七年级AQA科学课程中，化学部分引入的基本概念为未来的GCSE成功奠定基础。本文深入分析历年常见真题，揭示命题规律、评卷要求与常见陷阱。通过对物质状态、原子、元素、化合物、化学反应、酸和碱等考试题型进行拆解，我们会强化你的理解和应试技巧。每个小节都将剖析一道经典真题，解释最佳解题思路，并给出你提升分数所需要的标准答案逻辑。
1. States of Matter and Particle Theory | 物质状态与粒子理论
Past paper question: ‘Describe what happens to the particles in a solid when it is heated strongly enough to become a liquid. Explain why the temperature stays constant while melting.’ This two-part question tests both knowledge of particle behaviour and understanding of latent heat. The first part requires describing particle arrangement and motion changes; the second demands linking constant temperature to energy being used to overcome forces between particles.
真题题目：“描述固体在加热至液态时粒子的变化。解释熔化过程中温度保持恒定的原因。”这个两问的题目既考查粒子行为的知识，也考查对潜热的理解。第一部分需要描述粒子排布和运动的变化；第二部分则要求将恒温与能量用于克服粒子间作用力联系起来。
For a full-mark answer, you would state that particles in a solid are packed in a regular pattern and can only vibrate in fixed positions. As the solid is heated, the particles gain kinetic energy and vibrate faster. At the melting point, the vibrations become so strong that the forces holding the particles in place are overcome, and the particles can slide past each other, becoming a liquid. While melting, the added heat energy goes into breaking the bonds between particles rather than raising the kinetic energy, so the temperature does not rise.
要想获得满分，你应该说明固体中的粒子以规则方式紧密排列，只能在固定位置振动。随着固体受热，粒子获得动能并振动得更快。在熔点时，振动变得足够强，以至于粒子间维持位置的作用力被克服，粒子可以相互滑动，变成液体。熔化过程中，加入的热量用于破坏粒子间的键，而不是提高动能，因此温度不会升高。
Common mistake: Students often forget to mention the ‘regular pattern’ and ‘slide past each other’ descriptors, and many say ‘particles expand’ instead of ‘particles gain energy and vibrate more’. In the explanation part, they might incorrectly say the temperature stays the same because the solid is ‘using up heat’, without referencing the overcoming of forces. Using precise scientific language is key.
常见错误：学生经常忘记提到“规则排布”和“相互滑动”这样的描述，很多人说“粒子膨胀”而不是“粒子获得能量并振动加剧”。在解释部分，他们可能错误地说温度保持不变是因为固体“用光了热量”，而没有提到克服作用力。使用精确的科学语言是关键。
2. Atoms, Elements and Chemical Symbols | 原子、元素与化学符号
A typical question: ‘Give the chemical symbols for the following elements: sodium, potassium, iron, copper, and lead.’ This is a straightforward recall task, but many Year 7 students lose marks by confusing symbols, such as writing S for sodium (which is Na) or P for potassium (K). The correct answers are Na, K, Fe, Cu, and Pb. The real challenge often appears when they have to explain what an element is: ‘Explain why oxygen is considered an element, but water is not.’
常见题目：“写出下列元素的化学符号：钠、钾、铁、铜、铅。”这是一个简单的记忆任务，但许多七年级学生因混淆符号而失分，比如把钠写成 S（应为 Na），或把钾写成 P（应为 K）。正确答案是 Na、K、Fe、Cu 和 Pb。真正的挑战常出现在需要解释什么是元素时：“解释为什么氧气被视为元素，而水不是。”
The key definition: An element is a substance made up of only one type of atom. Oxygen (O₂) consists entirely of oxygen atoms, even if they are bonded in pairs, so it is an element. Water (H₂O) is a compound because it contains two types of atoms – hydrogen and oxygen – chemically bonded together. A good answer will state the definition first and then apply it to each substance, noting that water can be broken down into simpler substances but an element cannot.
关键定义是：元素是只由一种原子组成的物质。氧气（O₂）完全由氧原子构成，即使原子成对键合，它仍然是元素。水（H₂O）是化合物，因为它含有两种原子——氢和氧——通过化学键结合。一个好的答案会先陈述定义，然后将其应用到每种物质，并指出水可以分解成更简单的物质，而元素不能。
Examiner tip: When listing symbols, pay attention to capitalization. The first letter is always uppercase and any second letter is lowercase. ‘Co’ is cobalt, not carbon monoxide; ‘Pb’ comes from Latin plumbum. Mnemonic devices like ‘Little Naughty Kids Like Rabbits Playing’ (Na, K, Li, Rb, Cs – not all Year 7) can help, but for these five, simple repetition works best.
评卷提示：列出符号时要注意大小写。首字母必须大写，如有第二个字母则小写。“Co”是钴，不是一氧化碳；“Pb”源自拉丁语 plumbum。像“Naughty Kids Like Rabbits Playing”之类的记忆法对部分元素有效，但对这五种元素，简单的重复练习最有效。
3. The Periodic Table and Group Properties | 周期表与族性质
Past paper task: ‘Label the following on a blank periodic table: a metal, a non-metal, Group 1, and the period where sodium is found.’ This tests spatial awareness of the table’s layout. Sodium is in Group 1 (the alkali metals) and Period 3. Metals are on the left and centre, while non-metals are on the right. Students must then answer a follow-up: ‘Predict one property of an element in the same group as sodium.’
真题任务：“在空白周期表上标出：一种金属、一种非金属、第1族，以及钠所在的周期。”这考查对周期表布局的空间认识。钠位于第1族（碱金属）和第3周期。金属在左边和中间，非金属在右边。学生还需要回答追问：“预测与钠同族的元素的一种性质。”
Since elements in the same group have similar chemical properties, a correct prediction could be: ‘It will be soft and can be cut with a knife’, or ‘It will react vigorously with water to produce an alkali and hydrogen’, or ‘It will have low density’. The predictive power of the periodic table is a key concept. Marks are also awarded for stating that the element is a metal and has one electron in its outer shell, although Year 7 may not yet cover electron shells in detail – instead, focus on observable properties like shiny, conductors, and reactivity with water.
由于同族元素具有相似的化学性质，正确的预测可以是：“它质地柔软，可以用刀切割”，或者“它会与水剧烈反应生成碱和氢气”，或者“它的密度低”。周期表的预测能力是一个核心概念。学生还可以提到该元素是一种金属，且最外层有一个电子，不过七年级可能还没有详细接触电子层——此时可关注可观察的性质，例如有光泽、可导电和与水反应。
Common errors: Placing sodium in Group 2 or confusing periods with groups. Remember, periods are horizontal rows, and groups are vertical columns. Using mnemonic phrases like ‘Groups Go Up and Down, Periods Pass Left to Right’ helps. Also, when predicting properties, avoid vague answers like ‘it will react with water’ – specify ‘vigorously’ or ‘producing bubbles of gas’.
常见错误：把钠放在第2族，或混淆周期与族。记住，周期是横行，族是纵列。使用助记短句如“族上下走，周期左右通”有帮助。此外，预测性质时避免模糊回答，如“它会与水反应”——要具体说明“剧烈反应”或“产生气泡”。
4. Simple Chemical Reactions and Evidence | 简单化学反应与证据
Exam question: ‘A student mixes vinegar and baking soda in a flask. A fizzing sound is heard and the flask feels colder. Is this a chemical reaction? Give two pieces of evidence.’ This requires recognising indicators of a chemical change. The fizzing indicates a gas (carbon dioxide) is being produced, and the temperature decrease shows an endothermic reaction, meaning new substances are being formed.
考试题：“一名学生在烧瓶中混合白醋和小苏打。听到嘶嘶声，烧瓶感觉更冷了。这是化学反应吗？给出两个证据。”这需要学生识别化学变化的迹象。嘶嘶声表明产生了气体（二氧化碳），温度下降表明这是一个吸热反应，意味着有新物质生成。
A high-scoring answer: Yes, it is a chemical reaction. Evidence 1: Gas production (effervescence), which is a new substance being formed. Evidence 2: Temperature change (the mixture becomes colder), showing an energy transfer that accompanies the formation of new substances. Some students also mention a change in smell or a solid disappearing, but the two most obvious here are gas and temperature.
高分答案：是的，这是一个化学反应。证据1：气体生成（起泡），即新物质的形成。证据2：温度变化（混合物变冷），表明在形成新物质的同时发生了能量转移。有些学生还会提到气味变化或固体消失，但这里最明显的两个是气体和温度。
What to avoid: Do not just say ‘a fizz’ without linking it to new gas; do not confuse the cold feeling with ‘no reaction’. A thermal change is valid evidence. Also, remember that boiling water is not a chemical reaction, so evidence like ‘bubbles’ must be interpreted carefully – always link to new substance formation, not just physical state change. The reaction between vinegar (acetic acid) and baking soda (sodium hydrogencarbonate) produces sodium acetate, water, and carbon dioxide.
要避免的问题：不要只说“有嘶嘶声”而不将其与生成新气体联系起来；不要将变冷误解为“没有反应”。热量变化是有效的证据。还要记住，烧开水不是化学反应，因此像“气泡”这样的证据必须谨慎解读——一定要与生成新物质联系起来，而不仅仅是物理状态变化。白醋和烘焙苏打之间的反应生成醋酸钠、水和二氧化碳。
5. Acids, Alkalis and the pH Scale | 酸、碱与pH标度
Classic question: ‘You are given three colourless liquids labelled A, B, and C. Using only universal indicator, describe how you would determine which one is an acid, which is an alkali, and which is neutral. Include the expected colour changes.’ This practical-based question assesses understanding of the pH scale and indicator colour ranges. Universal indicator turns red in strong acid, orange/yellow in weak acid, green in neutral, blue in weak alkali, and purple/violet in strong alkali.
经典题目：“你有三种无色液体，分别标记为A、B和C。只使用通用指示剂，描述你如何确定哪一种是酸，哪一种是碱，哪一种是中性。请说明预期的颜色变化。”这道基于操作的题目考查对pH标度和指示剂颜色范围的理解。通用指示剂在强酸中变红，弱酸中呈橙色/黄色，中性呈绿色，弱碱中呈蓝色，强碱中呈紫色/紫罗兰色。
Model answer: Add a few drops of universal indicator to each liquid. The one that turns red or orange/yellow is the acid; the one that turns blue or purple is the alkali; the one that stays green is neutral. For full marks, specify that you would compare the colour against a pH colour chart to get an approximate pH value. You might also say that the acid would have a pH less than 7, the neutral exactly 7, and the alkali greater than 7.
标准答案：向每种液体中滴加几滴通用指示剂。变成红色或橙色/黄色的那一种是酸；变成蓝色或紫色的那一种是碱；保持绿色的那一种是中性。要拿到满分，需说明你会将颜色与pH色卡对比，以获得近似的pH值。你还可以补充说，酸的pH小于7，中性恰好为7，碱的pH大于7。
Common pitfalls: Students often confuse litmus with universal indicator. Litmus only tells you acid or alkali (red or blue), while universal indicator shows a range. Also, saying ‘the acid turns the indicator red’ is better than ‘the indicator turns the acid red’, but both are accepted. Remember: you cannot taste the liquids or touch them – safety is implicit. And never say ‘the neutral liquid has no colour’ – it is the indicator that gives colour; the original liquid is colourless.
常见陷阱：学生经常混淆石蕊和通用指示剂。石蕊只能告诉你酸性或碱性（红色或蓝色），而通用指示剂显示一个颜色范围。此外，“酸使指示剂变红”比“指示剂使酸变红”更标准的说法，不过两种都接受。记住：你不能品尝或触摸未知液体——安全至关重要。切勿说“中性液体没有颜色”——是指示剂呈现了颜色；原液体本是无色的。
6. Neutralisation and Word Equations | 中和反应与文字方程式
Exam question: ‘When an acid reacts with an alkali, the products are always salt and water. Write a word equation for the reaction between hydrochloric acid and sodium hydroxide solution. Then state the name of the salt formed.’ This a foundational skill in Year 7. The acid is hydrochloric acid, the alkali is sodium hydroxide. The salt formed will be sodium chloride (common table salt), plus water. The word equation is: hydrochloric acid + sodium hydroxide → sodium chloride + water.
考试题：“当酸与碱反应时，产物总是盐和水。写出盐酸与氢氧化钠溶液反应的文字方程式，并说明生成的盐的名称。”这是七年级的基础技能。酸是盐酸，碱是氢氧化钠。生成的盐将是氯化钠（常见的食盐），加上水。文字方程式为：盐酸 + 氢氧化钠 → 氯化钠 + 水。
To remember how to name the salt: the first part comes from the metal in the alkali (sodium), the second part from the acid. Hydrochloric acid gives chloride, sulfuric acid gives sulfate, nitric acid gives nitrate. So if the acid were sulfuric acid, the salt would be sodium sulfate. Word equations should always have the arrow pointing from reactants to products, and the names in full, not symbols. A common error is writing ‘NaCl’ instead of ‘sodium chloride’ when a word equation is specifically asked for.
记住盐的命名方式：第一部分来自碱中的金属（钠），第二部分来自酸。盐酸产生氯化物，硫酸产生硫酸盐，硝酸产生硝酸盐。因此如果酸是硫酸，盐将是硫酸钠。文字方程式必须用箭头从反应物指向生成物，并使用完整名称，而不是符号。常见错误是当题目明确要求文字方程式时，写成了“NaCl”而不是“氯化钠”。
Extension: The general pattern for neutralisation is acid + base → salt + water. Metals oxides and hydroxides are bases. Alkalis are soluble bases. This word equation might appear alongside a ‘state symbols’ requirement in later years, but for Year 7, just naming and writing the equation is sufficient. Practice with different combinations: sulfuric acid + potassium hydroxide → potassium sulfate + water.
拓展：中和反应的一般模式是酸 + 碱 → 盐 + 水。金属氧化物和氢氧化物是碱。碱是可溶的碱。该文字方程式在后续年级可能会伴随状态符号的要求，但在七年级，只要正确命名和书写方程式就足够了。用不同组合进行练习：硫酸 + 氢氧化钾 → 硫酸钾 + 水。
7. Separating Mixtures – Chromatography and Distillation | 混合物的分离——色谱与蒸馏
Common practical question: ‘A student uses paper chromatography to separate the colours in a black ink. She draws a pencil line and places a dot of ink on it. Explain why she must use pencil, not pen, and why the water level must be below the dot.’ This tests the rationale behind standard procedures. Pencil is insoluble and will not interfere with the results, whereas pen ink would dissolve and run. The water level must be below the dot so that the ink does not dissolve directly into the solvent reservoir, but instead the solvent travels up the paper and carries the ink components with it.
常见实验题：“一名学生用纸色谱法分离黑色墨水中的颜色。她用铅笔画了一条线，并在线上点了一个墨点。解释为什么必须用铅笔而不能用钢笔，以及为什么水面必须在墨点以下。”这考查标准操作背后的原理。铅笔不溶于水，不会干扰结果，而钢笔墨水会溶解并扩散。水面必须在墨点以下，这样墨水不会直接溶解到溶剂槽中，而是让溶剂沿纸上升并带着墨水组分一起移动。
Good answer: Pencil lead (graphite) is insoluble, so it will not be affected by the solvent and will not produce extra spots. If she used pen, the pen’s own colours would separate, contaminating the chromatogram. The water level stays below the dot to prevent the ink dot from washing off into the water. The separation occurs because different dyes have different solubilities and travel different distances, a process we measure using the Rf value, though that is more typical in Year 8 or GCSE.
好的答案：铅笔芯（石墨）不溶，所以不会被溶剂影响，也不会产生额外的斑点。如果她用钢笔，钢笔自己的颜色会分离，污染色谱图。水面保持在墨点以下是为了防止墨点被冲入水中。分离的发生是因为不同染料有不同的溶解度，移动的距离不同，我们用Rf值来衡量这个过程，不过那个在八年级或GCSE中更典型。
A second technique often tested is simple distillation. A question: ‘Describe how you could obtain pure water from a salt solution.’ You would mention heating the solution in a flask, water evaporates, steam travels through a condenser where it condenses back to liquid, and is collected in a beaker. The salt remains in the flask. Labeling a diagram with ‘thermometer’, ‘delivery tube’, ‘condenser’, ‘cold water in’, ‘cold water out’ is also common.
第二项常考的技术是简单蒸馏。题目：“描述如何从盐溶液中获得纯水。”你会提到将溶液放在烧瓶中加热，水蒸发，水蒸气通过冷凝管冷凝回液体，并收集在烧杯中。盐留在了烧瓶里。给示意图标注“温度计”、“导管”、“冷凝管”、“冷水入口”、“冷水出口”也很常见。
8. Combustion and the Fire Triangle | 燃烧与火三角
Past paper scenario: ‘A candle is covered with a glass jar and soon goes out. Explain why. Refer to the fire triangle in your answer.’ The fire triangle consists of fuel, oxygen, and heat. A candle flame requires all three. When you cover it with a jar, the oxygen supply is cut off, the flame uses up the remaining oxygen, and the candle extinguishes. The fuel (wax) and heat (from an initial source) are still present, but without oxygen, combustion stops.
真题情境：“用玻璃罐盖住蜡烛，蜡烛很快熄灭。请解释原因，并在回答中引用火三角。”火三角由燃料、氧气和热量组成。蜡烛火焰需三者齐备。当你用罐子盖住时，切断了氧气供应，火焰耗尽了剩余的氧气，蜡烛熄灭。燃料（蜡）和热量（初始火源提供）仍然存在，但没有氧气，燃烧停止。
Full answer: Combustion is a chemical reaction between a fuel and oxygen that releases heat. For a fire to continue, all three sides of the fire triangle (fuel, heat, oxygen) must be present. When the jar is placed over the candle, the limited oxygen inside is quickly used up, removing one side of the triangle. The candle goes out because the reaction can no longer take place. You could also mention that water or a fire blanket puts out fires by removing heat or oxygen respectively.
完整答案：燃烧是燃料与氧气发生的放热化学反应。要让火持续燃烧，必须同时具备火三角的三个要素（燃料、热量、氧气）。当玻璃罐罩住蜡烛时，内部有限的氧气很快被消耗殆尽，移除了火三角的一面。蜡烛熄灭是因为反应无法继续。你还可以提到用水或灭火毯灭火分别是通过移除热量或隔离氧气。
Examiners like to see the triangle explicitly named and each side linked to the situation. Avoid saying ‘the jar sucks up all the air’ or ‘the candle is suffocated’. Use scientific terms: oxygen depletion, removal of oxidiser, cessation of combustion. This question often comes with a diagram, be prepared to label or recognise the parts.
评卷人喜欢看到明确提及火三角，并将每一面与实际情况联系起来。避免说“罐子吸走了所有空气”或“蜡烛窒息了”。使用科学术语：氧气耗尽、移除氧化剂、燃烧停止。这道题常带有图示，要准备好标注或识别各部分。
9. Observations vs. Inferences in Chemical Tests | 化学测试中的观察与推理
A tricky type of question: ‘A student sees bubbles forming when magnesium is added to hydrochloric acid. State one observation and one inference.’ Observation: bubbles of a colourless gas are produced. Inference: a gas is being formed, and because it pops with a lighted splint, it is hydrogen. Many students confuse the two; an observation is something you can see, hear, or measure directly, while an inference is a conclusion based on evidence.
一种易错题型：“一名学生看到当把镁加入盐酸时有气泡产生。陈述一个观察和一个推理。”观察：产生了无色气泡。推理：有一种气体生成，因为它遇明火会发出爆鸣声，所以是氢气。许多学生会混淆两者；观察是你可以直接看到、听到或测量的东西，而推理是基于证据得出的结论。
If the question asks specifically for an observation, writing ‘hydrogen is produced’ would lose the mark, because you cannot see hydrogen; you see bubbles and then test to confirm. So a safe observation: ‘A gas is produced rapidly, and the magnesium ribbon disappears.’ The inference: ‘The gas is hydrogen; the reaction is exothermic (the test tube gets warm).’ Always stick to what your senses detect when asked for observations.
如果题目明确要求写出观察，写“产生了氢气”就会失分，因为你无法看到氢气；你看到气泡，然后测试确认。所以安全的观察是：“迅速产生气体，镁带消失。”推理是：“该气体是氢气；反应放热（试管变热）。”当被问及观察时，务必只陈述感官直接探测到的信息。
10. The Importance of Fair Testing and Variables | 公平测试与变量的重要性
Past paper question: ‘A student investigates the mass of salt that dissolves in water at different temperatures. Identify the independent, dependent, and one control variable.’ Independent: temperature of the water. Dependent: mass of salt that dissolves (or solubility). Control variables: volume of water, amount of salt added initially, stirring speed, same type of salt. This is a cornerstone of scientific enquiry.
真题问题：“一名学生研究不同温度的盐在水中的溶解质量。指出独立变量、因变量和一个控制变量。”独立变量：水的温度。因变量：溶解的盐的质量（或溶解度）。控制变量：水的体积、初始加入的盐的量、搅拌速度、盐的种类相同。这是科学探究的基础。
Wording matters: independent is what you change; dependent is what you measure or observe; control is what you keep the same to ensure a fair test. If the student heats water from 20°C to 80°C, the temperature is the independent variable. The mass of salt that actually dissolves is the dependent variable. Control variables could include using the same beaker, same mass of salt added each time, and letting the solution settle before measuring.
措辞很重要：独立变量是你改变的；因变量是你测量或观察的；控制变量是你为保持公平测试而保持不变的。如果学生将水从20°C加热到80°C，温度就是独立变量。实际溶解的盐的质量是因变量。控制变量可以包括使用相同的烧杯、每次加入等量的盐，以及测量前让溶液静置。
Examiners often ask you to explain why a variable must be controlled: for example, ‘Why must the same amount of salt be added to each beaker?’ So that the difference in dissolved mass is due only to temperature, not to the initial amount. This is crucial for validity. If an experiment is not a fair test, results are unreliable.
评卷人常会要求你解释为什么某一变量必须被控制：例如，“为什么每个烧杯中必须加入等量的盐？”这样溶解质量的差异就只能归因于温度，而不是初始的量。这对有效性至关重要。如果实验不是公平测试，结果就不可靠。
11. Exothermic and Endothermic Reactions in Context | 现实中的放热与吸热反应
A typical multiple-choice follow-up: ‘Which of the following is an endothermic process? A) burning wood, B) melting ice, C) respiration, D) explosion of TNT.’ The answer is B, melting ice. However, students must be able to distinguish between a physical change (melting) and a chemical reaction. Endothermic processes absorb heat from the surroundings, making them feel colder. In Year 7, we often meet the classic endothermic reaction: citric acid and sodium hydrogencarbonate, which feels cold to the touch.
典型的后续选择题：“以下哪个是吸热过程？A) 燃烧木材，B) 冰融化，C) 呼吸作用，D) TNT爆炸。”答案是B，冰融化。然而，学生必须能够区分物理变化（熔化）和化学反应。吸热过程从周围环境吸收热量，感觉变冷。在七年级，我们常常接触典型的吸热反应：柠檬酸与碳酸氢钠反应，摸起来是冷的。
In an exam, be prepared to describe an experiment to determine if a reaction is exothermic or endothermic. Measure the initial temperature of reactants, mix them, then measure the highest or lowest temperature reached. If temperature increases, it’s exothermic; if it decreases, it’s endothermic. Use a polystyrene cup as a calorimeter to reduce heat loss.
考试中，准备描述一个判断反应是放热还是吸热的实验：测量反应物的初始温度，混合它们，然后测量达到的最高或最低温度。如果温度升高，是放热；如果降低，是吸热。使用聚苯乙烯杯作为量热器以减少热量散失。
12. Applying Knowledge to Unfamiliar Contexts | 将知识应用于陌生情境
The highest marks in Year 7 chemistry go to students who can transfer concepts. A stretch question: ‘Dry ice is solid carbon dioxide. When it is left at room temperature, it turns directly into a gas without becoming a liquid. What is this process called? Explain why it is a physical change, not a chemical one.’ The process is sublimation. It is a physical change because no new substance is formed; carbon dioxide simply changes from solid to gas, and the reverse process (deposition) can occur without chemical alteration.
七年级化学中的最高分通常属于能够迁移概念的学生。一道拔高题：“干冰是固态二氧化碳。当它在室温下放置时，会直接变成气体且不经过液态。这个过程叫什么？解释为什么它是物理变化而不是化学变化。”这个过程是升华。它是物理变化，因为没有新物质生成；二氧化碳只是从固态变为气态，且逆过程（凝华）可以在不发生化学变化的情况下进行。
Students might be asked to compare this with ice melting and then evaporating. Ice melts at 0°C to water (liquid) and then water evaporates to water vapour. Dry ice sublimes at -78°C. The key is recognising that in both physical changes, the chemical composition remains H₂O or CO₂, while chemical changes rearrange atoms into new molecules.
学生可能会被要求将其与冰融化再蒸发进行比较。冰在0°C熔化成水（液态），然后水蒸发成水蒸气。干冰在-78°C升华。关键在于认识到在两个物理变化中，化学成分始终是H₂O或CO₂，而化学变化会将原子重新排列成新的分子。
This type of question tests the boundary between physical and chemical change brilliantly. Always ask: Are the same particles present before and after? If yes, it is physical. If new chemical bonds are formed, it is chemical.
这类问题出色地测试了物理变化和化学变化的界限。永远要问自己：反应前后是否还是同一些粒子？如果是，那就是物理变化。如果生成了新的化学键，那就是化学变化。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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