The States of Matter: Solids, Liquids and Gases | 物质三态：固体、液体和气体

📚 The States of Matter: Solids, Liquids and Gases | 物质三态：固体、液体和气体

Matter exists in three common states on Earth: solid, liquid and gas. These states are determined by the arrangement, energy and movement of particles. In this article, we will explore the kinetic particle theory, the properties of each state, and the changes that occur when substances are heated or cooled.

物质在地球上通常以三种状态存在：固态、液态和气态。这些状态由粒子的排列方式、能量和运动情况决定。本文将探讨动力学粒子理论、各状态的性质，以及物质在加热或冷却时发生的变化。

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1. The Particle Model | 粒子模型

The particle model describes matter as being made of tiny particles (atoms, molecules or ions) that are constantly moving. The strength of the forces between particles and the energy of the particles determine which state a substance is in.

粒子模型将物质描述为由不断运动的微小粒子（原子、分子或离子）构成的。粒子间作用力的强弱以及粒子能量的高低决定了物质处于哪种状态。

• In a solid, particles vibrate about fixed positions.

  在固体中，粒子在固定位置附近振动。

• In a liquid, particles are close together but can slide past each other.

  在液体中，粒子彼此靠近，但可以相互滑动。

• In a gas, particles are far apart and move freely at high speeds.

  在气体中，粒子相距很远，并以高速自由运动。

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2. Properties of Solids | 固体的特性

Solids have a definite shape and a definite volume. The particles are packed closely in a regular lattice, and the strong forces between them hold the structure rigidly.

固体有确定的形状和确定的体积。粒子紧密排列成规则的晶格，粒子间的强作用力使结构保持刚性。

• Solids cannot be compressed because there is no space between particles.

  固体不可压缩，因为粒子间没有空隙。

• Solids do not flow easily, though some can deform under pressure.

  固体不易流动，尽管有些固体在压力下会变形。

• The density of a solid is usually high because particles are close together.

  固体密度通常很高，因为粒子排列紧密。

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3. Properties of Liquids | 液体的特性

Liquids have a definite volume but no definite shape; they take the shape of the container. The particles are still close together, but they have enough energy to move past one another.

液体有确定的体积但没有确定的形状；它们会充满容器的形状。粒子仍然紧密相邻，但具有足够的能量可以相互移动。

• Liquids can flow and pour easily.

  液体可以流动和倾倒。

• Liquids are almost incompressible, but slightly compressible under very high pressure.

  液体几乎不可压缩，但在极高压下可略微压缩。

• Diffusion happens gradually in liquids as particles mix with each other.

  液体中会发生缓慢的扩散，因为粒子相互混合。

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4. Properties of Gases | 气体的特性

Gases have neither a definite shape nor a definite volume. They expand to fill the entire space available. The particles are far apart, and the forces between them are very weak.

气体既没有确定的形状，也没有确定的体积。它们会膨胀以充满所有可利用的空间。粒子相距很远，粒子间作用力非常弱。

• Gases are highly compressible because there is a lot of empty space between particles.

  气体高度可压缩，因为粒子间有大量空隙。

• Gases flow easily and mix rapidly by diffusion.

  气体容易流动，并通过扩散快速混合。

• The density of a gas is much lower than that of a solid or liquid.

  气体的密度远低于固体或液体。

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5. Changes of State | 状态变化

When a substance is heated, its particles gain kinetic energy and move faster. When cooled, particles lose energy and slow down. This leads to changes between states, which are physical changes because no new substance is formed.

当物质受热时，其粒子获得动能并运动加快。当冷却时，粒子失去能量并减速。这导致状态之间的变化，这些变化是物理变化，因为不会形成新物质。

solid ⇌ liquid ⇌ gas

Melting and boiling are endothermic processes (absorb heat). Freezing and condensation are exothermic processes (release heat).

熔化和沸腾是吸热过程（吸收热量）。凝固和冷凝是放热过程（释放热量）。

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6. Melting and Freezing | 熔化与凝固

Melting is the change from solid to liquid. The melting point is the temperature at which this occurs. For pure substances, the melting point is sharp. Freezing is the reverse process, where liquid becomes solid at the freezing point.

熔化是固态变为液态的过程。熔点是指发生这种变化的温度。对于纯净物质，熔点是明确的。凝固是相反过程，即液体在凝固点变为固体。

solid + heat → liquid ; liquid − heat → solid

During melting, the temperature stays constant until all the solid has melted. The heat energy is used to overcome forces between particles.

在熔化过程中，温度保持不变，直到所有固体熔化。热能用于克服粒子间的作用力。

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7. Boiling and Evaporation | 沸腾与蒸发

Boiling is the rapid change from liquid to gas that occurs throughout the liquid at the boiling point. Evaporation is a slower process that occurs only at the surface of a liquid, at temperatures below the boiling point.

沸腾是液体在沸点温度下整体发生的快速气化过程。蒸发是较缓慢的过程，仅在液体表面发生，温度低于沸点。

Boiling	Evaporation
Occurs at a fixed temperature (boiling point)	Occurs at any temperature above the liquid’s freezing point
Takes place throughout the liquid	Takes place only at the surface
Bubbles of gas form inside the liquid	No bubbles form inside the liquid
Requires heat to be supplied continuously	Can happen at room temperature; cooling effect occurs

Evaporation causes a cooling effect because the most energetic particles escape, lowering the average kinetic energy of the remaining liquid.

蒸发会产生冷却效应，因为最具能量的粒子逃逸，降低了剩余液体的平均动能。

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8. Condensation and Sublimation | 冷凝与升华

Condensation is the change from gas to liquid. It occurs when the gas cools and particles lose energy, allowing forces of attraction to pull them closer together. Sublimation is the change from solid directly to gas, and deposition is the reverse process. Iodine and carbon dioxide (dry ice) are examples of substances that sublimate.

冷凝是气态变为液态的过程。当气体冷却，粒子失去能量，使相互吸引的作用力将粒子拉近时发生。升华是固态直接变为气态，凝华是相反过程。碘和二氧化碳（干冰）是能升华的实例。

solid ⇌ gas (sublimation / deposition)

Sublimation requires heat energy to break the strong bonds between solid particles, moving them directly into the gas phase.

升华需要热能来破坏固体粒子间的强键，使其直接进入气相。

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9. Heating and Cooling Curves | 加热与冷却曲线

When the temperature of a pure substance is plotted against time as it is heated, the graph shows horizontal sections where the temperature stops rising. These plateaus correspond to melting (solid + liquid together) and boiling (liquid + gas together).

当纯净物质被加热时，将其温度随时间作图，图中会出现温度不再上升的平直段。这些平台对应熔化（固+液共存）和沸腾（液+气共存）。

• During a plateau, the absorbed heat is used to overcome attractive forces, not to raise temperature.

  在平台期间，吸收的热量用于克服吸引力，而不是升高温度。

• The slope of the curve depends on the mass, specific heat capacity and the heating rate.

  曲线的斜率取决于质量、比热容和加热速率。

• Cooling curves are the mirror image, with downward plateaus during freezing and condensation.

  冷却曲线是镜像关系，在凝固和冷凝过程中出现下降的平台。

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10. Diffusion and Gas Pressure | 扩散与气压

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. The rate of diffusion increases with temperature and decreases with particle mass. For example, ammonia gas (NH₃) diffuses faster than hydrogen chloride gas (HCl) because NH₃ molecules are lighter.

扩散是粒子从高浓度区域向低浓度区域的净运动。扩散速率随温度升高而增大，随粒子质量增大而减小。例如，氨气（NH₃）比氯化氢气体（HCl）扩散得快，因为 NH₃ 分子更轻。

Gas pressure is caused by particles colliding with the walls of the container. Increasing the number of particles or raising the temperature increases the pressure, provided the volume is constant.

气压是由粒子与容器壁碰撞引起的。在体积恒定的情况下，增加粒子数或升高温度都会使压强增大。

PV = constant (at constant temperature, for a fixed amount of gas)

This relationship is known as Boyle’s law, an important concept in understanding gas behaviour.

这一关系被称为波义耳定律，是理解气体行为的重要概念。

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