定义Definition
摩尔体积是单位物质的量的物质所占的体积，Vm = V/n。对气体而言，在相同温度和压强下，任何气体的摩尔体积近似相等：0 °C、101.325 kPa 时约为 22.4 L mol⁻¹，25 °C、100 kPa 时约为 24.8 L mol⁻¹。
Molar volume is the volume occupied by one mole of a substance, Vm = V/n. At the same temperature and pressure all gases have nearly the same molar volume: about 22.4 L mol⁻¹ at 0 °C and 101.325 kPa, and about 24.8 L mol⁻¹ at 25 °C and 100 kPa.
为什么各种气体相同Why it is the same for all gases
气体分子之间的距离远大于分子本身，气体体积主要由分子数、温度和压强决定，与分子种类基本无关，这就是阿伏伽德罗定律。由理想气体方程 pV = nRT 可得 Vm = RT/p。液体和固体中粒子紧密堆积，摩尔体积随物质而异。
Gas molecules are far apart compared with their size, so a gas's volume depends on the number of molecules, temperature and pressure, not on what the molecules are; this is Avogadro's law. From the ideal gas equation pV = nRT, Vm = RT/p. In liquids and solids the particles are packed together, so molar volume differs from substance to substance.
计算Calculation
n = V/Vm。例：0 °C、101.325 kPa 下 5.6 L O₂ 为 0.25 mol，质量 8.0 g。使用时必须注明温度和压强；实际气体在高压低温下偏离理想行为，摩尔体积会略小。
n = V/Vm. Example: 5.6 L of O₂ at 0 °C and 101.325 kPa is 0.25 mol, or 8.0 g. Always state the temperature and pressure; real gases at high pressure and low temperature deviate from ideal behaviour and have slightly smaller molar volumes.
年表Timeline
- 1811
阿伏伽德罗提出同温同压同体积气体含相同数目的分子
Avogadro proposes that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules
- 1834
克拉佩龙综合气体定律提出理想气体状态方程
Clapeyron combines the gas laws into the ideal gas equation
相关公式Formulas
例题Worked example
标况下 5.6 L O₂ 的物质的量为 5.6/22.4 = 0.25 mol，质量 8.0 g。
5.6 L of O₂ at STP is 0.25 mol, i.e. 8.0 g.