气体常数1865

使用的方程

• 理想气体常数出现于最简单的物态方程，理想气体定律，如下： （公式略）
• 其中： p 为一理想气体的压力 T 为其温度 V 为其摩尔体积
• 此式亦能被写成： pV=nRT

其中： V 为气体占有的体积 n 为气体的物质的量 R 同时也出现在能斯特方程及洛伦兹-洛伦茨方程中。

在国际单位制基本单位的重新定义后，其值为一精准数字： R=8.31446261815324 J/(K·mol)。

玻尔兹曼常数

玻尔兹曼常数 K_(B) （多记为 K）可以被用作其他形式的理想气体常数，在纯用粒子而不用摩尔计算时适用；其因数仅为阿伏伽德罗数，写成： （公式略）

可以将理想气体定律写成直接用玻尔兹曼常数表示的形式： PV=Nk_(B)T

其中 N=nN_(A) 是实际的粒子数。

个别气体常数

一种或多种气体混合物的个别气体常数（ R）可从通用气体常数求出，只需除以气体或混合物的摩尔质量（ M）。 R=R/M

只用符号R去代表个别气体常数也是相当普遍的。在这种情况下看 R 的内容与单位应该可以弄清它是哪种气体常数。例如在音速的方程中，通常是用个别气体常数表示的。

空气的个别气体常数为： （公式略）

美国标准大气层模型

美国标准大气层模型1976 (USSA1976)将通用气体常数（ R）定为： R=8.31432× 10³(N· m)/(kmol· K)

但是USSA1976亦指出这个值不符合阿伏伽德罗常量及玻尔兹曼常数的引用值。但是，USSA1976仍然使用这个R值去计算标准大气压。这个差在准确度上并不重要。当使用ISO的R值时，计算出的气压于11,000米时只多出了0.62帕斯卡（即相等于只是0.172米的差）及20,000米时多了0.292帕斯卡（即相等于只是0.338米的差）。

The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol R or R. It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per amount of substance, rather than energy per temperature increment per particle. The constant is also a combination of the constants from Boyle's law, Charles's law, Avogadro's law, and Gay-Lussac's law. It is a physical constant that is featured in many fundamental equations in the physical sciences, such as the ideal gas law, the Arrhenius equation, and the Nernst equation.

The gas constant is the constant of proportionality that relates the energy scale in physics to the temperature scale and the scale used for amount of substance. Thus, the value of the gas constant ultimately derives from historical decisions and accidents in the setting of units of energy, temperature and amount of substance. The Boltzmann constant and the Avogadro constant were similarly determined, which separately relate energy to temperature and particle count to amount of substance.

The gas constant R is defined as the Avogadro constant NA multiplied by the Boltzmann constant k (or kB): （公式略）

Since the 2019 revision of the SI, both NA and k are defined with exact numerical values when expressed in SI units. As a consequence, the SI value of the molar gas constant is exact.

Some have suggested that it might be appropriate to name the symbol R the Regnault constant in honour of the French chemist Henri Victor Regnault, whose accurate experimental data were used to calculate the early value of the constant. However, the origin of the letter R to represent the constant is elusive. The universal gas constant was apparently introduced independently by August Friedrich Horstmann (1873) and Dmitri Mendeleev who reported it first on 12 September 1874. Using his extensive measurements of the properties of gases, Mendeleev also calculated it with high precision, within 0.3% of its modern value.

The gas constant occurs in the ideal gas law: PV=nRT=mR_(specific)T, where P is the absolute pressure, V is the volume of gas, n is the amount of substance, m is the mass, and T is the thermodynamic temperature. Rspecific is the mass-specific gas constant. The gas constant is expressed in the same unit as molar heat.