This MedLibrary.org supplementary page on Gas constant is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
| Values of R | Units (V·P·T-1·n-1) |
|---|---|
| 8.314472 | J·K-1·mol-1 |
| 0.0820574587 | L·atm·K-1·mol-1 |
| 83.14472 | cm3·bar·mol-1·K-1 |
| 8.20574587 × 10-5 | m3·atm·K-1·mol-1 |
| 8.314472 | cm3·MPa·K-1·mol-1 |
| 8.314472 | L·kPa·K-1·mol-1 |
| 8.314472 | m3·Pa·K-1·mol-1 |
| 62.36367 | L·mmHg·K-1·mol-1 |
| 62.36367 | L·Torr·K-1·mol-1 |
| 83.14472 | L·mbar·K-1·mol-1 |
| 0.08314472 | L·bar·K-1·mol-1 |
| 1.987 | cal·K-1·mol-1 |
| 6.132440 | lbf·ft·K-1·g-mol-1 |
| 10.73159 | ft3·psi· °R-1·lb-mol-1 |
| 0.7302413 | ft3·atm·°R-1·lb-mol-1 |
| 998.9701 | ft3·mmHg·K-1·lb-mol-1 |
| 8.314472 × 107 | erg·K-1·mol-1 |
| 1716 (Air only) | ft·lb·°R-1·slug-1 |
| 286.9 (Air only) | N·m·kg-1·K-1 |
| 286.9 (Air only) | J·kg-1·K-1 |
The gas constant (also known as the molar, universal, or ideal gas constant, usually denoted by symbol R) is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation. It is equivalent to the Boltzmann constant, but expressed in units of energy (i.e. the pressure-volume product) per kelvin per mole (rather than energy per kelvin per particle).
Its value is:
- R = 8.314472(15) J · K-1 · mol-1
The two digits in parentheses are the uncertainty (standard deviation) in the last two digits of the value.
The gas constant occurs in the simplest equation of state, the ideal gas law, as follows:
where:
is the absolute pressure
is absolute temperature
is the volume the gas occupies
is the amount of gas (the number of gas molecules, usually in moles)
is the molar volume
The gas constant has the same units as specific entropy.
Contents |
Relationship with the Boltzmann constant
The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working in pure particle count, N, rather than number of moles, n, since
,
where NA is Avogadro's number. For example, the ideal gas law in terms of Boltzmann's constant is 
.
Specific gas constant
The specific gas constant of a gas or a mixture of gases (R) is given by the universal gas constant, divided by the molar mass (M) of the gas/mixture.
It is common to represent the specific gas constant by the symbol R. In such cases the context and/or units of R should make it clear as to which gas constant is being referred to. For example, the equation for the speed of sound is usually written in terms of the specific gas constant.
The specific gas constant of dry air is
US Standard Atmosphere
The US Standard Atmosphere, 1976 (USSA1976) defines the Universal Gas Constant as:[1][2]
The USSA1976 does recognize, however, that this value is not consistent with the cited values for the Avogadro constant and the Boltzmann constant.[2] This disparity is not a significant departure from accuracy, and USSA1976 uses this value of R for all the calculations of the standard atmosphere. When using the ISO value of R, the calculated pressure increases by only 0.62 pascals at 11,000 meters (the equivalent of a difference of only 0.174 meters – or 6.8 inches) and an increase of 0.292 pascals at 20,000 meters (the equivalent of a difference of only 0.338 meters – or 13.2 inches).
See also
References
- ^ "Standard Atmospheres". Retrieved on 2007-01-07.
- ^ a b U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976 (Linked file is 17 MiB).
External links
Wikipedia content modification information:
- This page was last modified on 7 October 2008, at 18:13.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Gas constant".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.