📚 Solids, Liquids & Gases | 固体、液体与气体
Everything around you is made of matter, and matter exists in three common states: solid, liquid, and gas. In the Edexcel IGCSE specification, you must be able to describe the properties of each state using the particle (kinetic) model, explain changes of state, interpret heating curves, and apply the gas laws. This article covers every key point in a structured revision format.
你周围的一切都由物质构成，而物质通常以三种状态存在：固体、液体和气体。在 Edexcel IGCSE 考纲中，你需要能够用粒子（分子运动）模型描述各状态的性质、解释物态变化、解读加热曲线，并运用气体定律。本文以结构化复习的形式涵盖所有关键考点。
1. The Particle Model | 粒子模型
The particle model (also called the kinetic model) treats all matter as being made up of extremely tiny particles — atoms, molecules, or ions. These particles are always in motion, and the strength of the forces between them determines whether the substance is a solid, a liquid, or a gas.
粒子模型（又称分子运动模型）将一切物质视为由极微小的粒子（原子、分子或离子）构成。这些粒子始终处于运动之中，粒子间作用力的强弱决定了物质是固体、液体还是气体。
All matter is made of particles: There is empty space between particles, though it is very small in solids and liquids.
所有物质都由粒子组成：粒子之间存在空隙，在固体和液体中空隙极小。
Particles are in constant motion: The motion energy (kinetic energy) increases with temperature.
粒子处于持续运动中：粒子的运动能量（动能）随温度升高而增大。
Forces between particles: Strong forces keep particles close together; weak forces allow them to move apart.
粒子间的作用力：强作用力使粒子紧密靠近；弱作用力则允许粒子彼此远离。
You should be able to explain macroscopic properties — such as density, compressibility, and shape — in terms of these microscopic ideas. Examiners award full marks only when you mention both the arrangement and the movement of particles.
你需要能够从微观角度解释宏观性质，如密度、可压缩性和形状。只有当答案同时提到粒子的排列方式和运动方式时，考官才会给满分。
2. Solids | 固体
A solid has a fixed shape and a fixed volume. It cannot be compressed easily and has a relatively high density. These properties are explained as follows:
固体具有固定的形状和固定的体积。固体不易被压缩，密度相对较高。这些性质可解释如下：
Arrangement: Particles are packed closely together in a regular, repeating lattice structure.
排列方式：粒子紧密堆叠，形成规则、重复的晶格结构。
Movement: Particles vibrate about fixed positions; they do not move from place to place.
运动方式：粒子在固定位置附近振动，不会从一个位置移动到另一个位置。
Forces: Very strong forces of attraction hold the particles firmly in place.
作用力：非常强的吸引力将粒子牢牢固定在原位。
Because the particles are tightly packed, solids are incompressible and have high densities. Because the particles cannot move past one another, solids maintain their shape even when a force is applied.
由于粒子紧密排列，固体不可压缩且密度高。由于粒子无法相互滑过，固体即使受力也能保持形状。
3. Liquids | 液体
A liquid has a fixed volume but no fixed shape — it takes the shape of its container. Liquids are also almost incompressible and usually have densities slightly lower than the corresponding solid.
液体具有固定的体积但没有固定的形状——它随容器形状而改变。液体也几乎不可压缩，密度通常略低于对应的固体。
Arrangement: Particles are close together but arranged randomly, without a regular pattern.
排列方式：粒子彼此靠近，但排列无序，没有规则图案。
Movement: Particles can slide past each other, allowing the liquid to flow and change shape.
运动方式：粒子可以相互滑过，使液体能够流动并改变形状。
Forces: The forces between particles are weaker than in solids but still strong enough to keep them in contact.
作用力：粒子间作用力比固体弱，但仍足以使粒子保持接触。
Liquids are difficult to compress because the particles are already almost touching. The random arrangement explains why liquids do not have a fixed shape, while the close packing explains why their volume is fixed.
液体难以压缩，因为粒子几乎已经相互接触。无序排列解释了液体为何没有固定形状，而紧密排列则解释了其体积为何固定。
4. Gases | 气体
A gas has neither a fixed shape nor a fixed volume. It expands to fill its container completely. Gases are highly compressible and have low densities.
气体既没有固定的形状，也没有固定的体积。它会膨胀以完全充满容器。气体极易压缩，密度很低。
Arrangement: Particles are very far apart compared to their own size, with mostly empty space between them.
排列方式：粒子之间的距离与其自身大小相比非常远，粒子之间大部分是空隙。
Movement: Particles move rapidly and randomly in straight lines until they collide with the container walls or with each other.
运动方式：粒子沿直线快速、杂乱地运动，直到与容器壁或其他粒子碰撞。
Forces: The forces between particles are negligible except during collisions.
作用力：除碰撞瞬间外，粒子间作用力可以忽略不计。
Gas pressure is caused by the many collisions of fast-moving particles with the container walls. When the temperature increases, particles move faster, collide more often and harder, so the pressure increases.
气体压强是由快速运动的粒子与容器壁频繁碰撞产生的。当温度升高时，粒子运动加快，碰撞更频繁、更有力，因此压强增大。
5. Changes of State | 物态变化
Substances can change from one state to another when energy is transferred to or from them. You must know the names of all six changes of state and the direction of each.
当物质获得或失去能量时，可以从一种状态转变为另一种状态。你必须掌握所有六种物态变化的名称及其方向。
| Change / 变化 | Direction / 方向 | Energy / 能量 |
| Melting 熔化 | Solid → Liquid 固体 → 液体 | Absorbed 吸收 |
| Freezing 凝固 | Liquid → Solid 液体 → 固体 | Released 释放 |
| Boiling 沸腾 | Liquid → Gas 液体 → 气体 | Absorbed 吸收 |
| Condensation 液化 | Gas → Liquid 气体 → 液体 | Released 释放 |
| Sublimation 升华 | Solid → Gas 固体 → 气体 | Absorbed 吸收 |
| Deposition 凝华 | Gas → Solid 气体 → 固体 | Released 释放 |
During melting and boiling, energy is absorbed to weaken or break the forces between particles. During freezing and condensation, energy is released as forces between particles form or strengthen. The temperature does not change during a pure substance's change of state.
在熔化和沸腾过程中，能量被吸收用于减弱或破坏粒子间作用力。在凝固和液化过程中，能量因作用力的形成或增强而释放。纯物质在物态变化期间温度保持不变。
6. Heating Curves | 加热曲线
A heating curve is a graph of temperature against time as a substance is heated at a constant rate. You must be able to read melting and boiling points from the graph and explain each section in terms of particles.
加热曲线是以恒定速率加热物质时，温度随时间变化的图像。你需要能够从图中读出熔点和沸点，并从粒子角度解释每一段。
Rising sections: The substance is in one state whose particles gain kinetic energy, so temperature rises.
上升段：物质处于单一状态，粒子获得动能，因此温度上升。
Flat sections (plateaus): The substance is changing state. Energy supplied breaks/forms forces between particles rather than increasing kinetic energy, so temperature stays constant.
平台段：物质正在发生物态变化。供给的能量用于破坏/形成粒子间作用力，而不是增加动能，因此温度保持不变。
Melting point: temperature of the first flat section; Boiling point: temperature of the second flat section.
On a cooling curve, the same plateaus appear in reverse. The reverse processes (freezing, condensation) release exactly the same amount of energy that was absorbed during melting and boiling.
在冷却曲线上，同样的平台按相反顺序出现。逆向过程（凝固、液化）释放的能量恰好等于熔化、沸腾时吸收的能量。
7. Latent Heat | 潜热
The energy transferred during a change of state without a temperature change is called latent heat. In IGCSE Edexcel, you need to understand the concept and use the formula for specific latent heat.
物态变化过程中温度不变但发生转移的能量称为潜热。在 Edexcel IGCSE 中，你需要理解这一概念并运用比潜热公式。
Specific latent heat of fusion: energy needed to change 1 kg of solid into liquid (or released when liquid freezes) at the melting point.
熔化比潜热：在熔点时，使 1 kg 固体变为液体（或液体凝固时释放）所需的能量。
Specific latent heat of vaporisation: energy needed to change 1 kg of liquid into gas (or released when gas condenses) at the boiling point.
汽化比潜热：在沸点时，使 1 kg 液体变为气体（或气体液化时释放）所需的能量。
joules, m is mass in kilograms, and L is the specific latent heat in joules per kilogram.
能量计算使用公式 E = mL，其中 E 为能量（单位：焦耳），m 为质量（单位：千克），L 为比潜热（单位：焦耳每千克）。
E = m × L
a specific latent heat of fusion of 334 000 J/kg, calculate E = 0.5 × 334 000 = 167 000 J.
例如，若要计算使 0.5 kg 冰熔化所需能量（熔化比潜热为 334 000 J/kg），则 E = 0.5 × 334 000 = 167 000 J。
8. Evaporation vs Boiling | 蒸发与沸腾
Evaporation and boiling are often confused, but Edexcel expects you to distinguish them clearly with at least four points of comparison.
蒸发和沸腾经常被混淆，但 Edexcel 期望你至少能从四个方面清楚地区分二者。
| Feature 特征 | Evaporation 蒸发 | Boiling 沸腾 |
| Location 发生位置 | Only at the surface 仅液体表面 | Throughout the liquid 整个液体内部 |
| Temperature 温度条件 | Any temperature below boiling point 沸点以下的任何温度 | At the boiling point only 仅在沸点 |
| Speed 速率 | Slow process 缓慢过程 | Rapid process 快速过程 |
| Bubbles 气泡 | No bubbles 无气泡 | Bubbles form in the liquid 液体内产生气泡 |
Evaporation explains the cooling effect: the fastest-moving (most energetic) molecules escape from the surface, leaving behind slower-moving molecules, so the average kinetic energy — and therefore temperature — of the remaining liquid decreases.
蒸发解释了冷却效应：运动最快（能量最高）的分子从表面逸出，留下运动较慢的分子，因此剩余液体的平均动能——即温度——降低。
9. Gas Laws | 气体定律
For Edexcel IGCSE, you need to know Boyle's Law, Charles's Law, and the Pressure Law, and be able to perform calculations using them. Temperatures must be in kelvin (K) in all three laws.
对于 Edexcel IGCSE，你需要掌握玻意耳定律、查理定律和压强定律，并能用它们进行计算。三个定律中的温度都必须使用开尔文（K）。
Boyle's Law (constant temperature): For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume.
玻意耳定律（温度恒定）：一定质量的气体在温度不变时，压强与体积成反比。
P₁V₁ = P₂V₂
Charles's Law (constant pressure): For a fixed mass of gas at constant pressure, volume is directly proportional to absolute temperature.
查理定律（压强恒定）：一定质量的气体在压强不变时，体积与绝对温度成正比。
V₁ / T₁ = V₂ / T₂
The Pressure Law (constant volume): For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature.
压强定律（体积恒定）：一定质量的气体在体积不变时，压强与绝对温度成正比。
P₁ / T₁ = P₂ / T₂
For example, 20 °C = 293 K. Never substitute Celsius values directly into these equations.
将摄氏度转换为开尔文时，加 273：T(K) = θ(°C) + 273。例如，20 °C = 293 K。切勿将摄氏温度直接代入这些公式。
At the particle level, if a gas is compressed into a smaller volume, particles collide with the walls more frequently, so pressure increases. If temperature rises at fixed volume, particles move faster and hit the walls harder, so pressure increases.
从粒子层面看，如果气体被压缩到更小体积，粒子与器壁的碰撞更频繁，因此压强增大。如果体积不变而温度升高，粒子运动加快，撞击器壁更有力，因此压强增大。
10. Summary Comparison | 对比总结
The table below summarises the key properties of the three states of matter. Memorising this table is an efficient way to secure quick marks in the exam.
下表总结了三种物态的关键性质。记住这张表是在考试中快速得分的有效方法。
| Property 性质 | Solid 固体 | Liquid 液体 | Gas 气体 |
| Shape 形状 | Fixed 固定 | Takes container shape 随容器 | Fills container 充满容器 |
| Volume 体积 | Fixed 固定 | Fixed 固定 | Variable 可变 |
| Compressibility 可压缩性 | Very low 极低 | Very low 极低 | High 高 |
| Density 密度 | High 高 | High 高 | Low 低 |
| Particle spacing 粒子间距 | Very close 很近 | Close 近 | Far apart 很远 |
| Particle motion 粒子运动 | Vibrate in place 原位振动 | Slide past each other 相互滑过 | Rapid, random motion 快速无序运动 |
When answering exam questions, always link the observable property to the particle behaviour. For example, "Gases are compressible because the particles are far apart with empty space between them that can be reduced."
回答考题时，务必将可观察的性质与粒子行为联系起来。例如："气体可压缩，因为粒子相距很远，中间存在可减小的空隙。"
You are now equipped with all the core knowledge for the Solids, Liquids & Gases topic in Edexcel IGCSE Physics. Practice past-paper questions on heating curves and gas-law calculations, and always write your answers using the particle model. Good luck with your revision!
你现在已经掌握了 Edexcel IGCSE 物理"固体、液体与气体"主题的全部核心知识。多做关于加热曲线和气体定律计算的历年真题，并始终使用粒子模型来书写答案。祝你复习顺利！
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