📚 The Gaseous State | 气体状态
Gases are one of the three common states of matter, characterised by particles that are widely separated, in constant random motion, and able to fill any container. In A-level Chemistry, understanding the gaseous state involves quantitative relationships among pressure, volume, temperature and amount of gas, as well as the kinetic theory that explains these observations at the molecular level.
气体是物质三种常见状态之一，其特征是粒子间距很大、持续无规则运动并能够充满任何容器。在 A-level 化学中，理解气体状态涉及压强、体积、温度与气体物质的量之间的定量关系，以及从分子层面解释这些现象的动理论。
1. States of Matter and the Gaseous State | 物质状态与气体状态
In the gaseous state, particles are much further apart than in solids or liquids, so the forces of attraction between them are negligible under ordinary conditions. This explains why gases have low density, are highly compressible, and undergo rapid diffusion.
在气体状态下，粒子之间的距离比固体或液体中远得多，因此在通常条件下粒子间的吸引力可以忽略不计。这解释了为什么气体密度低、高度可压缩并且能够快速扩散。
A gas has no fixed shape or volume; it expands to fill its container completely. The pressure exerted by a gas is caused by collisions of gas particles with the walls of the container.
气体没有固定的形状或体积；它会膨胀并完全充满容器。气体施加的压强是由气体粒子与容器壁碰撞引起的。
Because gas particles are in constant, random motion, a sample of gas can be described by four macroscopic variables: pressure, volume, temperature and number of moles.
由于气体粒子处于持续无规则运动中，一定量气体可以用四个宏观变量来描述：压强、体积、温度和物质的量。
2. Pressure, Volume, Temperature and Amount | 压强、体积、温度与物质的量
In calculations, pressure is usually expressed in pascals (Pa) or kilopascals (kPa), volume in cubic metres (m³) or cubic decimetres (dm³), and temperature in kelvin (K). The kelvin scale must be used because all gas laws are based on absolute temperature.
在计算中，压强通常以帕斯卡（Pa）或千帕（kPa）表示，体积以立方米（m³）或立方分米（dm³）表示，温度以开尔文（K）表示。必须使用开尔文温标，因为所有气体定律都基于绝对温度。
One mole of any ideal gas occupies about 24.0 dm³ at room temperature and pressure (RTP, usually 25 °C and 1 atm or 101 kPa). This molar volume is a useful shortcut when conditions are specified.
在室温和常压下（RTP，通常为 25 °C 和 1 atm 或 101 kPa），1 mol 任何理想气体的体积约为 24.0 dm³。当题目给定条件时，这个摩尔体积是一个很有用的换算捷径。
Temperature conversion is essential: T (K) = T (°C) + 273. A common exam error is to use Celsius temperatures in pV = nRT, which gives incorrect results.
温度换算是关键：T (K) = T (°C) + 273。考试中常见错误是在 pV = nRT 中使用摄氏温度，这会导致结果错误。
3. Boyle’s Law: Pressure-Volume Relationship | 波义耳定律：压强-体积关系
Boyle’s law states that for a fixed amount of gas at constant temperature, the pressure of a gas is inversely proportional to its volume: pV = constant, or p ∝ 1/V.
波义耳定律指出，对于恒温下的一定量的气体，气体的压强与体积成反比：pV = 常数，或 p ∝ 1/V。
If a gas expands from volume V₁ to V₂ while the temperature and amount remain constant, the new pressure can be found using p₁V₁ = p₂V₂. A graph of p against 1/V gives a straight line through the origin.
如果气体在温度和物质的量不变的情况下从体积 V₁ 膨胀到 V₂，新压强可以用 p₁V₁ = p₂V₂ 求得。p 对 1/V 作图会得到一条过原点的直线。
This relationship means that compressing a gas into a smaller volume increases the frequency of collisions with the container walls, raising the pressure.
这一关系意味着，将气体压缩到较小体积会增加气体与容器壁碰撞的频率，从而提高压强。
4. Charles’s Law: Volume-Temperature Relationship | 查理定律：体积-温度关系
Charles’s law states that for a fixed amount of gas at constant pressure, the volume is directly proportional to the absolute temperature: V ∝ T, or V/T = constant.
查理定律指出，对于恒压下的一定量的气体，体积与绝对温度成正比：V ∝ T，或 V/T = 常数。
The relationship can be written as V₁/T₁ = V₂/T₂. If a gas is heated at constant pressure, the particles gain kinetic energy, move faster, and push outward to occupy a larger volume.
该关系可以写为 V₁/T₁ = V₂/T₂。如果在恒压下加热气体，粒子获得动能，运动加快，并向外推动以占据更大的体积。
A graph of volume against Celsius temperature is a straight line that extrapolates to -273 °C, which defines the absolute zero of the kelvin scale.
体积对摄氏温度作图是一条直线，外推至 -273 °C，该点定义了开尔文温标的绝对零度。
5. Avogadro’s Law and Molar Volume | 阿伏伽德罗定律与摩尔体积
Avogadro’s law states that at constant temperature and pressure, equal volumes of all gases contain the same number of moles. Thus V ∝ n.
阿伏伽德罗定律指出，在相同温度和压强下，体积相同的所有气体含有相同的物质的量。因此 V ∝ n。
This law allows molar volume to be used in stoichiometric gas calculations. For example, at RTP, 24.0 dm³ of hydrogen gas and 24.0 dm³ of carbon dioxide both contain 1 mol of molecules, despite their very different molar masses.
该定律使摩尔体积可用于气体参与的化学计量计算。例如，在 RTP 下，24.0 dm³ 氢气和 24.0 dm³ 二氧化碳都含有 1 mol 分子，尽管它们的摩尔质量差别很大。
For a chemical reaction involving gases, the mole ratio can be read directly from the volume ratio when all gas volumes are measured at the same temperature and pressure.
对于涉及气体的化学反应，当所有气体体积在相同温度和压强下测量时，物质的量之比可以直接从体积比得出。
6. The Ideal Gas Equation pV = nRT | 理想气体方程 pV = nRT
Combining Boyle’s law, Charles’s law and Avogadro’s law gives the ideal gas equation:
综合波义耳定律、查理定律和阿伏伽德罗定律，可以得到理想气体方程：
pV = nRT
In this equation, p is pressure in pascals (Pa), V is volume in cubic metres (m³), n is amount in moles (mol), T is absolute temperature in kelvin (K), and R is the gas constant, 8.31 J K⁻¹ mol⁻¹.
在此方程中，p 是压强，单位为帕斯卡（Pa）；V 是体积，单位为立方米（m³）；n 是物质的量，单位为摩尔（mol）；T 是绝对温度，单位为开尔文（K）；R 是气体常数，8.31 J K⁻¹ mol⁻¹。
When using pV = nRT, volumes must be converted from cm³ or dm³ to m³: 1 m³ = 1 × 10⁶ cm³ and 1 dm³ = 1 × 10⁻³ m³. Pressure in kPa must be multiplied by 1000 to become Pa.
使用 pV = nRT 时，体积必须从 cm³ 或 dm³ 换算为 m³：1 m³ = 1 × 10⁶ cm³，1 dm³ = 1 × 10⁻³ m³。压强若以 kPa 为单位，必须乘以 1000 转换为 Pa。
The ideal gas equation can be used to calculate molar mass (M = mRT / pV), density (ρ = pM / RT), or the molar volume under non-standard conditions.
理想气体方程还可以用于计算摩尔质量（M = mRT / pV）、密度（ρ = pM / RT）或非标准条件下的摩尔体积。
7. Dalton’s Law of Partial Pressures | 道尔顿分压定律
Dalton’s law states that in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of each component gas: p_total = p_A + p_B + p_C +
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