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Gas constant
| Value of R[1] | Unit |
|---|---|
| SI units | |
| 8.31446261815324 | J⋅K−1⋅mol−1 |
| 8.31446261815324 | m3⋅Pa⋅K−1⋅mol−1 |
| 8.31446261815324 | kg⋅m2⋅s−2⋅K−1⋅mol−1 |
| Other common units | |
| 8314.46261815324 | L⋅Pa⋅K−1⋅mol−1 |
| 8.31446261815324 | L⋅kPa⋅K−1⋅mol−1 |
| 0.0831446261815324 | L⋅bar⋅K−1⋅mol−1 |
| 8.31446261815324×107 | erg⋅K−1⋅mol−1 |
| 0.730240507295273 | atm⋅ft3⋅lbmol−1⋅°R−1 |
| 10.731577089016 | psi⋅ft3⋅lbmol−1⋅°R−1 |
| 1.985875279009 | BTU⋅lbmol−1⋅°R−1 |
| 297.031214 | inH2O⋅ft3⋅lbmol−1⋅°R−1 |
| 554.984319180 | torr⋅ft3⋅lbmol−1⋅°R−1 |
| 0.082057366080960 | L⋅atm⋅K−1⋅mol−1 |
| 62.363598221529 | L⋅torr⋅K−1⋅mol−1 |
| 1.98720425864083... | cal⋅K−1⋅mol−1 |
| 8.20573660809596...×10−5 | m3⋅atm⋅K−1⋅mol−1 |
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):
-
- = 6.02214076×1023 mol−1 × 1.380649×10−23 J⋅K−1
- = 8.31446261815324 J⋅K−1⋅mol−1
Since the 2019 revision of the SI, both NA and k are defined with exact numerical values when expressed in SI units.[2] 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 Clausius' student, A.F. Horstmann (1873)[3][4] and Dmitri Mendeleev who reported it first on 12 September 1874.[5] Using his extensive measurements of the properties of gases,[6][7] Mendeleev also calculated it with high precision, within 0.3% of its modern value.[8]
The gas constant occurs in the ideal gas law: 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.
- ^ "2022 CODATA Value: molar gas constant". The NIST Reference on Constants, Units, and Uncertainty. NIST. May 2024. Retrieved 2024-05-18.
- ^ Newell, David B.; Tiesinga, Eite (2019). The International System of Units (SI). NIST Special Publication 330. Gaithersburg, Maryland: National Institute of Standards and Technology. doi:10.6028/nist.sp.330-2019. S2CID 242934226.
- ^ Jensen, William B. (July 2003). "The Universal Gas Constant R". J. Chem. Educ. 80 (7): 731. Bibcode:2003JChEd..80..731J. doi:10.1021/ed080p731.
- ^ "Ask the Historian: The Universal Gas Constant — Why is it represented by the letter R?" (PDF).
- ^ Mendeleev, Dmitri I. (September 12, 1874). "An exert from the Proceedings of the Chemical Society's Meeting on Sept. 12, 1874". Journal of Russian Chemical-Physical Society, Chemical Part. VI (7): 208–209.
- ^ Mendeleev, Dmitri I. (1875). On the elasticity of gases [Объ упругости газовъ]. A.M. Kotomin, St.-Petersburg.
- ^ D. Mendeleev. On the elasticity of gases. 1875 (in Russian)
- ^
Mendeleev, Dmitri I. (March 22, 1877). "Mendeleef's researches on Mariotte's law 1". Nature. 15 (388): 498–500. Bibcode:1877Natur..15..498D. doi:10.1038/015498a0.
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