Solids, Liquids and Gases | 固体、液体与气体

📚 Solids, Liquids and Gases | 固体、液体与气体

Everything around us is made of matter, and matter usually exists in one of three familiar states: solid, liquid, or gas. In your Edexcel IGCSE Science course, understanding how particles behave in these states is essential for explaining properties such as shape, volume, density, and pressure. This revision guide walks through the particle model, changes of state, density, fluid pressure, and the gas laws, helping you build confidence for Paper 1 and Paper 2 questions.

我们周围的一切都由物质构成，而物质通常以三种我们熟悉的状态之一存在：固态、液态或气态。在 Edexcel IGCSE 科学课程中，理解粒子在这些状态下的行为对于解释形状、体积、密度和压强等性质至关重要。这篇复习指南将带你梳理粒子模型、状态变化、密度、流体压强以及气体定律，帮助你在试卷一和试卷二中稳操胜券。

1. Introduction to States of Matter | 物质状态导论

Matter is classified into solids, liquids, and gases based on shape and volume. Solids have a fixed shape and volume. Liquids have a fixed volume but take the shape of their container. Gases have no fixed shape or volume and expand to fill any container. These differences arise from the arrangement and motion of particles in each state.

根据形状和体积，物质可分为固体、液体和气体。固体有固定的形状和体积；液体有固定的体积，但形状随容器而变；气体既没有固定的形状也没有固定的体积，会膨胀并充满整个容器。这些差异源于各状态中粒子的排列方式和运动状态。

2. The Particle Model | 粒子模型

All matter consists of tiny, constantly moving particles – atoms, molecules, or ions. The particle model is a simple way to explain the properties of solids, liquids, and gases. The key ideas are: particles are in constant motion, there are spaces between them, and there are forces of attraction holding them together. In solids, particles are closely packed in a regular pattern, vibrating in fixed positions. In liquids, particles are still close together but can slide past each other. In gases, particles are far apart and move rapidly in random directions.

所有物质都由微小的、不断运动的粒子——原子、分子或离子——组成。粒子模型是解释固体、液体和气体性质的一种简单方法。其核心思想是：粒子在不停地运动，粒子间存在间隙，并且有吸引力将它们维系在一起。在固体中，粒子紧密排列成规则的结构，只能在固定位置上振动。在液体中，粒子仍然紧靠在一起，但可以相互滑动。在气体中，粒子相距很远，并沿着随机方向快速运动。

3. Solids: Structure and Properties | 固体的结构与性质

In a solid, strong forces of attraction hold particles close together in a rigid, regular arrangement. The particles cannot move freely; they only vibrate about fixed positions. This explains why solids have a definite shape and volume, are virtually incompressible, and usually have high density. When heated, solids expand slightly because the particles vibrate more and move slightly further apart.

在固体中，强大的吸引力将粒子束缚在刚性的规则排列中。粒子不能自由移动，只能在固定位置附近振动。这就解释了为什么固体有固定的形状和体积，几乎不可压缩，并且通常密度较高。加热时，固体略微膨胀，因为粒子振动加剧，间距略微增大。

4. Liquids: Structure and Properties | 液体的结构与性质

Liquid particles are still held together by attractive forces, but these forces are weaker than in solids, allowing particles to slide past one another. This gives liquids a fixed volume but no fixed shape. Liquids are only slightly compressible because particles are already close together. Density is generally lower than that of solids of the same substance (with water as a notable exception where ice is less dense). Liquids flow and can diffuse, though more slowly than gases.

液体粒子仍然通过吸引力结合在一起，但这些力比固体中的弱，使得粒子能够相互滑动。因此，液体有固定的体积但没有固定的形状。液体几乎不可压缩，因为粒子已经靠得很近。其密度通常低于同种物质的固体（水是一个显著例外，冰的密度反而更小）。液体可以流动并能扩散，但速度比气体慢。

5. Gases: Structure and Properties | 气体的结构与性质

In a gas, the forces of attraction between particles are negligible. Particles move rapidly and randomly, colliding with each other and with the walls of their container. Gases have no fixed shape or volume; they expand to fill available space. They are easily compressed because the particles are widely spaced. Gases have low densities and diffuse quickly to mix with other gases. The pressure a gas exerts is due to the force of countless collisions on surfaces.

在气体中，粒子间的吸引力几乎可以忽略不计。粒子在快速、随机地运动，并相互碰撞或与容器壁碰撞。气体既无固定形状也无固定体积，会膨胀填满可用空间。它们很容易被压缩，因为粒子间距很大。气体密度低，并能迅速扩散与其他气体混合。气体产生的压强源于无数粒子对表面的碰撞力。

6. Changes of State | 状态变化

. During a change of state, the temperature remains constant even though heating continues – ergy. Sublimation (solid → gas directly) also occurs for some substances, such as dry ice.

物质可以通过获得或失去能量而改变状态。熔化（固体→液体）和沸腾/蒸发（液体→气体）需要吸收能量，属于吸热过程。冷凝（气体→液体）和凝固（液体→固体）会释放能量，属于放热过程。在状态变化期间，即使持续加热，温度也保持不变——这部分能量用于打破或形成粒子间的结合，而不是增加动能。某些物质还存在升华现象（固体直接变为气体），如干冰。

7. Density: Definition and Calculation | 密度的定义与计算

Density ρ (rho) is defined as mass per unit volume. The formula is:

Density = Mass ÷ Volume

For a regular solid, volume is calculated from dimensions; for irregular solids, use a displacement method with a measuring cylinder. A liquid’s density can be found by measuring its mass and volume.

广告 / Sponsored

密度 ρ 定义为单位体积的质量，公式为：

密度 = 质量 ÷ 体积

用符号表示为 ρ = m / V，其中质量 m 的单位是千克（kg）或克（g），体积 V 的单位是立方米（m³）或立方厘米（cm³）。密度的国际单位是 kg/m³，但 IGCSE 课程中常用 g/cm³。要记住换算：1 g/cm³ = 1000 kg/m³。对于规则固体，体积可通过尺寸计算；对于不规则固体，可使用量筒排水法测量。液体的密度可通过测量其质量和体积求得。

8. Pressure: Definition and in Fluids | 压强的定义与流体压强

Pressure is the force acting per unit area acting at right angles to a surface. The formula is:

Pressure = Force ÷ Area

d gases), pressure increases with depth because the weight of the fluid above exerts a force. The pressure at a depth h in a liquid of density ρ is given by:

Pressure difference = ρ × g × h

where g is the gravitational field strength (9.8 N/kg on Earth). This explains why dams are thicker at their bases and why deep-sea divers experience greater pressure.

压强是垂直作用在单位面积上的力，公式为：

压强 = 力 ÷ 面积

（p = F / A），单位为帕斯卡（Pa），1 Pa = 1 N/m²。在流体（液体和气体）中，压强随着深度的增加而增大，因为上方流体的重量会产生压力。在密度为 ρ 的液体中，深度 h 处的压强差可通过下式计算：

压强差 = ρ × g × h

其中 g 为重力场强度（地球上约为 9.8 N/kg）。这就解释了为什么水坝底部较厚，以及深海潜水员会承受更大的压力。

9. Gas Pressure and the Particle Model | 气体压强与粒子模型

Gas pressure is caused by the collision of gas particles with the walls of their container. Each collision exerts a tiny force; billions of collisions per second add up to produce a steady pressure. If the temperature increases, the average kinetic energy of the particles increases, so they move faster and collide harder and more frequently – thus pressure rises if volume is fixed. If a gas is compressed into a smaller volume, particles hit the walls more often, also increasing pressure.

气体压强是由气体粒子与容器壁的碰撞引起的。每次碰撞产生微小的力；每秒钟数十亿次碰撞累积起来，就形成了稳定的压强。如果温度升高，粒子的平均动能增加，它们运动得更快，碰撞得更猛烈、更频繁——因此，若体积固定，压强就会上升。若气体被压缩至更小的体积，粒子撞击壁面的次数增多，同样会使压强升高。

10. Boyle's Law: Pressure-Volume Relationship | 波义耳定律：压强与体积的关系

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume:

p ∝ 1 / V or p₁V₁ = p₂V₂

This means if you halve the volume, the pressure doubles, provided temperature stays the same. Boyle’s law is explained by the particle model: in a smaller volume, particles have less distance to travel between collisions with the walls, so they strike more frequently, increasing pressure. Graphs of p against V give a curve; p against 1/V gives a straight line through the origin.

对于一定质量、温度恒定的气体，其压强与体积成反比：

p ∝ 1 / V 或 p₁V₁ = p₂V₂

这意味着，如果体积减半，在温度不变的条件下，压强会加倍。波义耳定律可以通过粒子模型解释：在更小的体积内，粒子在两次器壁碰撞之间行进的距离更短，因此碰撞更频繁，压强便增大。p-V 图像是一条曲线；p-1/V 图像则是一条过原点的直线。

11. Temperature and Gas Volume (Charles's Law) | 温度与气体体积（查理定律）

For a fixed mass of gas at constant pressure, the volume is directly proportional to the absolute temperature (measured in kelvin):

V ∝ T or V₁ / T₁ = V₂ / T₂

Charles’s law shows that if the kelvin temperature doubles, the volume doubles. Heating a gas gives the particles more kinetic energy, so they push harder on the walls; if the container can expand (e.g., a piston), the volume increases to keep pressure constant. Graphs of volume against temperature (℃) give a straight line that extrapolates to zero volume at -273℃ – the concept of absolute zero.

对于一定质量、压强恒定的气体，其体积与热力学温度（开尔文温标）成正比：

V ∝ T 或 V₁ / T₁ = V₂ / T₂

查理定律表明，如果开尔文温度加倍，体积也会加倍。加热气体使粒子动能增大，因此它们对器壁的推力更强；如果容器可以膨胀（如活塞），体积就会增大，从而保持压强恒定。体积-温度（℃）图像是一条直线，将直线延长至体积为零处，对应的温度为 -273℃——这便是绝对零度的概念。

12. Absolute Zero and the Kelvin Scale | 绝对零度与开尔文温标

Absolute zero is the lowest possible temperature, where particles have the minimum kinetic energy and cannot move slower. It is 0 kelvin (0 K), equivalent to -273.15℃ (IGCSE usually uses -273℃). The kelvin scale is the absolute temperature scale used in gas law calculations. To convert from Celsius to kelvin: add 273. The kelvin scale means temperature is directly proportional to average particle kinetic energy, making it essential for understanding thermal physics.

绝对零度是最低的可能温度，此时粒子具有最小的动能，无法运动得更慢。绝对零度为 0 开尔文（0 K），相当于 -273.15℃（IGCSE 中通常使用 -273℃）。开尔文温标是气体定律计算中所使用的绝对温标。从摄氏度换算为开尔文的方法是加上 273。开尔文温标意味着温度与粒子的平均动能成正比，这对理解热物理至关重要。

Published by TutorHao | IGCSE Science Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）