📚 The Gaseous State | 气态
Gases play a fundamental role in chemistry, from the atmosphere to industrial processes. Understanding the behaviour of gases allows us to predict how they respond to changes in temperature, pressure, and volume. The study of the gaseous state combines empirical gas laws, the ideal gas equation, and the kinetic molecular theory to explain macroscopic properties at the molecular level.
气体在化学中扮演着基础性角色，从大气到工业过程无不涉及。理解气体的行为使我们能够预测它们在温度、压力、体积变化时的响应。对气态的研究将经验气体定律、理想气体方程和分子动理论结合起来，从分子层面解释宏观性质。
1. Properties of Gases | 气体的性质
Gases are one of the three common states of matter. Unlike solids and liquids, gases do not have a definite shape or volume; they completely fill any container they occupy. Gas particles move rapidly and randomly, colliding with each other and with the container walls. These collisions give rise to pressure. Gases have much lower densities than liquids and solids, and they are highly compressible because of the large spaces between particles.
气体是物质三种常见状态之一。与固体和液体不同，气体没有固定的形状和体积，它们会完全充满所在的容器。气体粒子快速且随机地运动，彼此碰撞并与容器壁碰撞。这些碰撞产生了压强。气体的密度远低于液体和固体，且由于粒子间有较大的空间，气体具有高度的可压缩性。
2. Measuring Gas Pressure | 气体压强的测量
Pressure is defined as force per unit area. In the laboratory, gas pressure is measured using a manometer or a barometer. The SI unit is the pascal (Pa), but other units such as atmospheres (atm), millimetres of mercury (mmHg) and bar are also common.
压强定义为单位面积上的力。实验室中用压力计或气压计测量气体压强。国际单位是帕斯卡(Pa)，但大气压(atm)、毫米汞柱(mmHg)、巴(bar)等单位也常用。下表总结了常见压强单位及其换算关系。
| Unit | Symbol | Equivalent in pascals (Pa) |
|---|---|---|
| pascal | Pa | 1 |
| atmosphere | atm | 101 325 |
| millimetre of mercury | mmHg | 133.3 |
| bar | bar | 100 000 |
3. Boyle's Law | 波义耳定律
Boyle' stant temperature, the pressure is inversely proportional to the volume. Mathematically, p ∝ 1/V, so pV = constant. For two sets of conditions, this can be written as p₁V₁ = p₂V₂.
p₁V₁ = p₂V₂
波义耳定律指出，对于一定质量的气体，在温度不变的情况下，压强与体积成反比。数学上，p ∝ 1/V，因此 pV = 常数，或者表达为 p₁V₁ = p₂V₂。若用曲线表示，等温条件下压强–体积图为双曲线。
4. Charles's Law | 查理定律
Charles' is gives V/T = constant, or V₁/T₁ = V₂/T₂. It is essential to use the Kelvin scale; if temperature is measured in Celsius, the relationship is not directly proportional.
V₁/T₁ = V₂/T₂
查理定律指出，在压强不变的条件下，一定质量气体的体积与其绝对温度（开尔文）成正比。因此 V/T = 常数，也可写成 V₁/T₁ = V₂/T₂。必须使用开尔文温标，因为用摄氏温标时体积与温度并非正比关系。外推体积至零时，对应的温度为 –273.15 °C，即绝对零度。
5. Avogadro's Law and Molar Volume | 阿伏伽德罗定律与摩尔体积
Avogadro's law states that equal volumes of all gases, at the same temperature and pressure, contain the same number of particles. Hence, the volume of a gas is directly proportional to the amount in moles (n) at constant T and P: V ∝ n. The molar volume of an ideal gas depends on the chosen standard conditions. Under standard temperature and pressure (STP) of 273 K and 100 kPa, as used in current Cambridge International specifications, one mole of an ideal gas occupies 22.7 dm³. At room temperature and pressure (RTP, about 293 K and 1 atm), the molar volume is approximately 24.0 dm³.
V ∝ n (at constant T and P)
阿伏伽德罗定律指出，在相同温度和压强下，相同体积的任何气体均含有相同数目的粒子。因此，在温度和压强恒定时，气体的体积与物质的量(n)成正比。理想气体的摩尔体积取决于所选的标准条件。在现行剑桥国际大纲中，标准温度压力(STP)为 273 K、100 kPa，此时一摩尔理想气体的体积为 22.7 dm³。而在室温和常压(RTP，约 293 K，1 atm)下，摩尔体积约为 24.0 dm³。
6. The Ideal Gas Equation | 理想气体方程
Combining Boyle's law, Charles's law and Avogadro' kelvin, and R = 8.31 J K⁻¹ mol⁻¹. When using kilopascals and cubic decimetres (1 m³ = 1000 dm³), the numerical value of R remains 8.31, but its units become kPa dm³ K⁻¹ mol⁻¹.
pV = nRT R = 8.31 J K⁻¹ mol⁻¹
综合波义耳定律、查理定律与阿伏伽德罗定律，可得到理想气体方程：pV = nRT，其中 R 为摩尔气体常数。采用国际单位制时，p 以帕斯卡(Pa)为单位，V 以立方米(m³)为单位，n 为物质的量(mol)，T 为开尔文温度，则 R = 8.31 J K⁻¹ mol⁻¹。若压强用千帕(kPa)、体积用立方分米(dm³)，数值仍为 8.31，单位变为 kPa dm³ K⁻¹ mol⁻¹。
7. Dalton's Law of Partial Pressures | 道尔顿分压定律
In a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases. Each gas behaves as if it occupies the whole volume alone. Mathematically, Ptotal = P₁ + P₂ + P₃ + … bserved total pressure is the sum of the dry gas pressure and the water vapour pressure: Pdry gas = Patm – Pwater vapour.
Ptotal = P₁ + P₂ + P₃ + …
在互不反应的气体混合物中，总压强等于各组分气体分压之和。每种气体都如同单独占据整个容器体积一样。数学表达为 Ptotal = P₁ + P₂ + P₃ + …。该定律在排水集气法中特别有用，此时观测到的总压强等于干燥气体分压与水蒸气分压之和：P干燥气体 = P大气压 – P水蒸气。
8. Kinetic Molecular Theory of Gases |
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