物质的状态
化学· 1.1–1.7（第 S1 部分 1(a)）· 25 分钟阅读
1. 1. 物质三态的粒子模型★☆☆☆☆⏱ 5 min
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粒子模型
该模型认为所有物质都由不断运动的微小粒子构成，粒子的排列方式、运动状态和能量由物质的物态决定。
每种物态都有独特的粒子性质：
- 固体：粒子规则紧密排列在固定位置，仅在固定位置附近振动，动能较低。固体有固定的形状和体积，不可被压缩。
- 液体：粒子无规则排布、紧密堆积，没有固定的排列模式。粒子可以相互滑动、缓慢移动，动能中等。液体有固定的体积，形状随容器变化，难以被压缩。
- 气体：粒子无规则排布，间距极大，粒子间存在大量空隙。粒子向各个方向自由快速运动，动能很高。气体没有固定的形状和体积，极易被压缩。
描述液态水和水蒸气中粒子的排列方式与运动状态的差异。
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对比排列方式：液态水的粒子间距很小，无规则排布，粒子间几乎没有空隙。水蒸气的粒子间距很大，无规则排布，粒子间存在大量空隙。
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对比运动状态：液态水的粒子相互滑动、缓慢移动。水蒸气的粒子向各个方向自由快速运动。
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对比能量：水蒸气粒子的动能远高于液态水的粒子。
2. 2. 物态间的相互转化★★☆☆☆⏱ 6 min
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Interconversion Name | Starting State | End State | Energy Change | Particle Change |
|---|---|---|---|---|
Melting | Solid | Liquid | Gained | Particles gain energy, vibrate faster, break free of fixed positions, move around each other |
Freezing | Liquid | Solid | Lost | Particles lose energy, move slower, form regular fixed positions, only vibrate |
Boiling | Liquid | Gas | Gained | Particles gain enough energy to break all bonds between them, move freely rapidly |
Evaporation | Liquid | Gas | Gained | Only surface particles gain enough energy to escape into the gas phase |
Condensation | Gas | Liquid | Lost | Particles lose energy, move slower, move close together, form a liquid |
Sublimation | Solid/Gas | Gas/Solid | Gained/Lost | Particles gain/lose enough energy to skip the liquid phase entirely |
解释熔融态铁冷却凝固为固态铁块时粒子发生的变化。
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确定转化类型：凝固（液态转化为固态）
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能量变化：粒子在冷却过程中失去热能
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运动变化：粒子运动速率减慢，不再相互滑过
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排列变化：粒子形成规则、紧密堆积的固定结构，仅在自身固定位置附近振动
3. 3. 扩散与稀释现象解释★★☆☆☆⏱ 5 min
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扩散作用
由于粒子的无规则运动，粒子从高浓度区域向低浓度区域发生的净移动。
有色溶液的稀释（例如将紫色高锰(VII)酸钾溶液加入水中）与气体扩散（例如溴蒸气与空气混合）都可以用粒子的无规则运动解释。当溶质粒子和溶剂粒子做无规则运动时，随着时间推移它们会在整个可占据空间内均匀分布，最终形成均一的混合物。
一名学生将一滴蓝色食用色素滴入盛有静止水的烧杯中。10分钟后，整杯水都变为浅蓝色。请用粒子模型解释该现象。
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指明过程：这是粒子扩散导致的稀释现象
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描述粒子运动：蓝色食用色素的溶质粒子与水的溶剂粒子都在持续做无规则运动
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解释结果：随着时间推移，蓝色溶质粒子从高浓度区域（色素滴）均匀扩散到低浓度区域（其余的水），直到整杯溶液呈现均一的浅蓝色。
4. 4. 溶液相关术语与溶解度 [仅高阶内容要求]★★★☆☆HL 专属⏱ 9 min
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饱和溶液
在指定温度下，溶剂中无法再溶解更多溶质的溶液，此时加入的额外溶质会以未溶解的固体形式留存。
Solute: Substance that dissolves in a solvent
Solvent: Liquid that a solute dissolves in
Solution: Homogeneous mixture of solute and solvent
Solubility: Maximum mass of solute that dissolves in 100g of solvent at a fixed temperature, units = g/100g solvent
溶解度曲线以溶解度（y轴单位：g/100g水）为纵轴，温度（x轴单位：°C）为横轴绘图。绝大多数固态溶质的溶解度随温度升高而增大，而气体的溶解度随温度升高而减小。你可以从曲线上读取任意温度下的溶解度数值，也可以通过插值法计算出指定质量的溶质形成饱和溶液时对应的温度。
测定指定温度下溶解度的实验步骤：1. 将100g水加热至目标温度，2. 边搅拌边少量多次加入溶质，直到溶质不再溶解，3. 过滤除去未溶解的溶质，4. 将滤液蒸发至完全干燥，5. 称量干燥后的溶质质量，即可得到以g/100g水为单位的溶解度。
硝酸钾的溶解度曲线显示，60°C时硝酸钾的溶解度为110g/100g水。请问在60°C时，250g水中最多可以溶解多少克硝酸钾以配制成饱和溶液？
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已知溶解度的定义为每100g水中的溶质质量：60°C时100g水最多溶解110g硝酸钾
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计算每1g水可溶解的溶质质量：g 每1g水
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乘以250g水：g
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结论：60°C时250g水中最多可溶解275g硝酸钾。
5. 常见陷阱
错误做法:
Saying particles expand or get bigger when heated
原因:
Particles do not change size when heated; only the space between them increases
正确做法:
State that particles gain kinetic energy, move faster, and the distance between particles increases, causing the substance to expand
错误做法:
Confusing boiling and evaporation as the same process
原因:
Boiling occurs at a fixed boiling point throughout the liquid, while evaporation occurs only at the surface at any temperature below boiling point
正确做法:
Explicitly distinguish the two processes using the points above when asked to compare them
错误做法:
Forgetting to state the temperature when giving solubility values
原因:
Solubility changes significantly with temperature, so values are meaningless without a stated temperature
正确做法:
Always include the temperature when writing or quoting solubility values in g/100g solvent
错误做法:
Describing diffusion as particles 'choosing' to move to low concentration areas
原因:
Diffusion happens due to random, constant movement of particles, not intentional movement
正确做法:
Explain that particles move randomly, so over time they spread evenly across the available space, resulting in net movement from high to low concentration
错误做法:
Saying gases cannot be compressed because their particles are small
原因:
Gases are compressible because there are large gaps between gas particles
正确做法:
Explain that gas particles are very far apart, so the space between them can be reduced when pressure is applied, making gases easy to compress
6. 速查表
Concept | Key Details | Exam Must-Include |
|---|---|---|
Solid particles | Regular, tightly packed, vibrate around fixed positions, low energy | Arrangement, movement, energy |
Liquid particles | Random, close together, slide past each other, medium energy | Arrangement, movement, energy |
Gas particles | Random, far apart, move freely rapidly, high energy | Arrangement, movement, energy |
State interconversions | Melting, freezing, boiling, evaporation, condensation, sublimation | Name, energy change, particle changes |
Diffusion explanation | Net movement from high to low concentration due to random particle movement | Mention random movement of particles, concentration gradient |
Solubility (Higher only) | g per 100g solvent at fixed temperature, solubility curves y = solubility, x = temperature | Include units and temperature, label axes correctly for curves |
7. 常见问题
沸腾和蒸发的区别是什么？
沸腾发生在固定的沸点，在整个液体内部进行，过程十分剧烈。蒸发仅发生在液体表面，可在任何低于沸点的温度下进行，过程较为缓慢。
物质受热时粒子的体积会变大吗？
不会。粒子本身的大小保持不变。物质受热时，粒子获得动能，运动速率加快，粒子间的间距增大，因此物质整体发生膨胀。
爱德思 IGCSE 化学中溶解度的常用单位是什么？
本考试大纲中，溶解度的单位统一为每100g溶剂（通常为水）中溶解的溶质克数，该考点仅出现在高阶化学试题中。
深入阅读
下一步
Now you have mastered the states of matter and particle model, you are ready to move on to the next topic in Edexcel IGCSE Chemistry Principles of Chemistry: separation techniques, where you will use your understanding of particle properties to explain how to separate mixtures of different states of matter. This foundational particle model knowledge will also be critical for later topics, including chemical bonding, rates of reaction, and gas chemistry. For higher tier students, your solubility curve skills will be used when you learn about crystallisation separation methods and chemical calculations involving solutions. Make sure you practice describing particle changes for state interconversions and explaining diffusion experiments, as these are common 2-3 mark questions in both Paper 1C and Paper 2C exams.