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{| class="wikitable" style="float: right;"
! Values of ''R''
! Units <br /> [[Ideal gas law|(V·P·T<sup>-1</sup>·n<sup>-1</sup>)]]
|- [[International Organization for Standardization | ISO]]
| 8.314472
| [[Joule|J]]·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 0.0820574587
| [[Liter|L]]·[[atmosphere (unit)|atm]]·[[Kelvin|K]]<sup>-1</sup>·[[Mole (unit)|mol]]<sup>-1</sup>
|-
| 83.14472
| [[centimeter|cm]]<sup>3</sup>·[[bar (unit)|bar]]·[[mole (unit)|mol]]<sup>-1</sup>·[[Kelvin|K]]<sup>-1</sup>
|-
| 8.20574587 × 10<sup>-5</sup>
| m<sup>3</sup>·atm·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 8.314472
| cm<sup>3</sup>·MPa·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 8.314472
| L·k[[Pascal (unit)|Pa]]·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 8.314472
| m<sup>3</sup>·[[Pascal (unit)|Pa]]·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 62.36367
| L·[[mmHg]]·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 62.36367
| L·Torr·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 83.14472
| L·mbar·K<sup>-1</sup>·mol<sup>-1</sup>
|-
|-
| 0.08314472
| L·bar·K<sup>-1</sup>·mol<sup>-1</sup>
|-

| 1.987
| [[calorie|cal]]·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 6.132440
| [[foot-pound|lbf]]·ft·K<sup>-1</sup>·g-mol<sup>-1</sup>
|-
| 10.73159
| ft<sup>3</sup>·psi· [[Rankine scale|°R]]<sup>-1</sup>·[[lb-mol]]<sup>-1</sup>
|-
| 0.7302413
| ft<sup>3</sup>·atm·°R<sup>-1</sup>·lb-mol<sup>-1</sup>
|-
| 998.9701
| ft<sup>3</sup>·mmHg·K<sup>-1</sup>·lb-mol<sup>-1</sup>
|-
| 8.314472 × 10<sup>7</sup>
| erg·K<sup>-1</sup>·mol<sup>-1</sup>
|-
| 1716 '''(Air only)'''
| ft·lb·°R<sup>-1</sup>·[[slug (unit)|slug]]<sup>-1</sup>
|-
| 286.9 '''(Air only)'''
| N·m·kg<sup>-1</sup>·K<sup>-1</sup>
|-
| 286.9 '''(Air only)'''
| J·kg<sup>-1</sup>·K<sup>-1</sup>
|}
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 (unit)|mole]]'' (rather than energy per kelvin per ''particle'').

Its value is:
:'''''R'' = 8.314472(15) J &middot; K<sup>-1</sup> &middot; mol<sup>-1</sup>'''
The two digits in [[Bracket|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:
:<math>P = \frac{nRT}{V} = \frac{RT}{V_{\rm m}}</math>
where:
: <math>P\,\!</math> is the absolute [[pressure]]
: <math>T\,\!</math> is absolute [[thermodynamic temperature|temperature]]
: <math>V\,\!</math> is the volume the gas occupies
: <math>n\,\!</math> is the amount of gas (the number of gas molecules, usually in [[mole (unit)|mole]]s)
: <math>V_{\rm m}\,\!</math> is the [[molar volume]]

The gas constant has the same units as specific [[entropy]].
===Relationship with the Boltzmann constant===
The [[Boltzmann constant]] ''k<sub>B</sub>'' (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
:<math>\qquad R=N_A k_B\,\!</math>,
where <math>N_A</math> is [[Avogadro constant|Avogadro's number]].
For example, the ideal gas law in terms of Boltzmann's constant is <math>PV=Nk_BT\,\!</math>.

===Specific gas constant===

The '''specific gas constant''' of a gas or a mixture of gases (<math>R</math>) is given by the universal gas constant, divided by the [[molar mass]] (<math>M</math>) of the gas/mixture.
:<math> R = \frac{\bar{R}}{M} </math>

It is common to represent the specific gas constant by the symbol <math>R</math>. In such cases the context and/or units of <math>R</math> should make it clear as to which gas constant is being referred to. For example, the equation for the [[speed of sound#speed in ideal gases and in air|speed of sound]] is usually written in terms of the specific gas constant.

The specific gas constant of dry [[air]] is
:<math>R_\mathrm{dry\,air} = 287.05 \frac{\mbox{J}}{\mbox{kg} \cdot \mbox{K}}</math>

==US Standard Atmosphere==
The [[US Standard Atmosphere]], 1976 (USSA1976) defines the Universal Gas Constant as:<ref>{{cite web |url=http://www.sworld.com.au/steven/space/atmosphere/ |title=Standard Atmospheres |accessdate=2007-01-07}}</ref><ref name="USSA1976">[http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf U.S. Standard Atmosphere], 1976, U.S. Government Printing Office, Washington, D.C., 1976 (Linked file is 17 MiB).</ref>

:<math>\bar{R} = 8.31432\times 10^3 \frac{\mathrm{N \cdot m}}{\mathrm{kmol \cdot K}} </math>

The USSA1976 does recognize, however, that this value is not consistent with the cited values for the Avogadro constant and the Boltzmann constant.<ref name="USSA1976"/> 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 [[International Organization for Standardization|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 ==
* [[Boltzmann constant]]
* [[measurement uncertainty|Standard measurement uncertainty]]

==References==

<!--See [[Wikipedia:Footnotes]] for an explanation of how to generate footnotes using the <ref(erences/)> tags-->
<references/>

== External links ==
* [http://physics.nist.gov/cgi-bin/cuu/Value?r|search_for=gas+constant Gas Constant CODATA Value] at [[NIST]]
* [http://physics.nist.gov/cgi-bin/cuu/Value?k|search_for=boltzmann Boltzmann Constant CODATA Value] at [[NIST]]

[[Category:Gases|Constant]]
[[Category:Physical constants]]
[[Category:Amount of substance]]

[[ar:ثابت الغازات العام]]
[[bs:Univerzalna gasna konstanta]]
[[bg:Универсална газова константа]]
[[cs:Molární plynová konstanta]]
[[da:Gaskonstant]]
[[de:Universelle Gaskonstante]]
[[et:Universaalne gaasikonstant]]
[[es:Constante universal de los gases ideales]]
[[eo:Universala gaskonstanto]]
[[fa:ثابت عمومی گازها]]
[[fr:Constante universelle des gaz parfaits]]
[[ko:기체 상수]]
[[it:Costante dei gas]]
[[he:קבוע הגזים]]
[[lt:Dujų konstanta]]
[[hu:Egyetemes gázállandó]]
[[nl:Gasconstante]]
[[ja:気体定数]]
[[mr:वैश्विक वायू एकक]]
[[no:Gasskonstant]]
[[nn:Gasskonstant]]
[[pl:Stała gazowa]]
[[pt:Constante universal dos gases perfeitos]]
[[ru:Универсальная газовая постоянная]]
[[sk:Univerzálna plynová konštanta]]
[[sl:Splošna plinska konstanta]]
[[fi:Kaasuvakio]]
[[sv:Allmänna gaskonstanten]]
[[th:ค่าคงตัวของแก๊ส]]
[[vi:Hằng số khí]]
[[uk:Газова стала]]
[[zh:氣體常數]]

Revision as of 00:40, 13 October 2008

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