📚 States of Matter and Phase Changes | 物质状态与相变
Understanding why ice melts, water boils and perfume spreads across a room begins with one powerful idea: all matter is made of tiny particles. This article develops the particle model of solids, liquids and gases, explains the energy changes during melting, boiling, evaporation and sublimation, and applies the model to diffusion, gas pressure and Brownian motion. It is designed for Cambridge science students who need clear, exam-focused explanations.
理解冰为何融化、水为何沸腾、香水为何在房间中扩散，都始于一个强大的概念：所有物质都由微小粒子组成。本文建立固体、液体和气体的粒子模型，解释熔化、沸腾、蒸发和升华过程中的能量变化，并将该模型应用于扩散、气体压强和布朗运动。文章为剑桥科学学生提供清晰、紧扣考点的讲解。
1. Introduction to the Particle Model | 粒子模型简介
The particle model states that all matter is made of extremely small particles, such as atoms, molecules or ions. These particles are too small to see directly, but their collective behaviour explains the macroscopic properties of materials. In a solid, liquid or gas, the particles are in constant motion, and the amount of movement depends on temperature. The model does not show the exact size or shape of real particles, but it is a useful scientific approximation.
粒子模型指出，所有物质都由极小的粒子组成，例如原子、分子或离子。这些粒子小到无法直接观察，但它们的集体行为可以解释材料的宏观性质。在固体、液体或气体中，粒子都在不断运动，运动程度取决于温度。该模型并不表示真实粒子的确切大小或形状，但它是一种有用的科学近似。
The model is powerful because it links microscopic behaviour to what we can measure. For example, the fact that gases are easy to compress can be explained by the large spaces between gas particles. Similarly, the fixed shape of a solid is explained by strong forces holding particles in a regular pattern. When scientists use the particle model, they are not claiming that particles are literally tiny balls; instead, they are using a simplified picture to make predictions and explain observations.
该模型之所以强大，是因为它将微观行为与我们可以测量的现象联系起来。例如，气体容易被压缩这一事实可以用气体粒子之间的大空间来解释。同样，固体的固定形状可以用强作用力将粒子保持在规则排列中来解释。当科学家使用粒子模型时，他们并不是声称粒子真的是微小的球体；相反，他们是在使用简化的图像进行预测和解释观察结果。
2. Properties of Solids, Liquids and Gases | 固体、液体和气体的性质
The three common states of matter have distinct macroscopic properties. Solids have a fixed shape and a fixed volume. Liquids have a fixed volume but take the shape of the bottom of their container. Gases have neither a
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