Molar gas constant: Difference between revisions
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In [[chemistry]] and [[physics]], the '''molar gas constant''' ''R'' is a physical constant | In [[chemistry]], [[chemical engineering]] and [[physics]], the '''molar gas constant''' ''R'' is a fundamental physical constant which appears 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 the [[Boltzmann constant]] (''k<sub>B</sub>'') times [[Avogadro's constant]] (''N''): ''R'' = ''k''<sub>B</sub>''N''<sub>A</sub>. | ||
It has a defining value of:<ref>[http://physics.nist.gov/cgi-bin/cuu/Value?r Molar gas constant] Obtained on 16 December, 2007 from the NIST website</ref> | |||
The constant | :'''''R'' = 8.314472(15) J · K<sup>-1</sup> · mol<sup>-1</sup>''' | ||
:<math> | |||
The gas constant occurs in the [[ideal gas law]] as follows: | |||
</math> | |||
where '' | :<math>P = \frac{nRT}{V} = \frac{RT}{V_{\rm m}}</math> | ||
where: | |||
:''P'' is the gas absolute [[pressure]] | |||
:''T'' is gas absolute) [[temperature]] | |||
: ''V'' is the volume the gas occupies | |||
: ''n'' is the number of [[mole (unit)|moles]] of gas | |||
: ''V<sub>m</sub>'' is the [[molar volume]] | |||
== Notation for the gas constant == | == Notation for the gas constant == | ||
The gas constant defined in this article is the universal gas constant, <math>R</math>, that applies to any gas. There is also a | The gas constant defined in this article is the universal gas constant, <math>R</math>, that applies to any gas. There is also a specific gas constant, which can be denoted as <math>R_s</math>. The specific gas constant is defined as <math>R_s = R/M</math> where <math>M</math> is the [[molecular weight]]. | ||
Unfortunately, many authors in the technical literature sometimes use <math>R</math> as the gas | Unfortunately, many authors in the technical literature sometimes use <math>R</math> as the specific gas constant without denoting it as such or stating that it is the specific gas constant. This can and does lead to confusion for many readers. | ||
==Reference== | ==Reference== | ||
{{reflist}} | |||
Revision as of 23:33, 1 April 2008
In chemistry, chemical engineering and physics, the molar gas constant R is a fundamental physical constant which appears 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 the Boltzmann constant (kB) times Avogadro's constant (N): R = kBNA.
It has a defining value of:[1]
- R = 8.314472(15) J · K-1 · mol-1
The gas constant occurs in the ideal gas law as follows:
where:
- P is the gas absolute pressure
- T is gas absolute) temperature
- V is the volume the gas occupies
- n is the number of moles of gas
- Vm is the molar volume
Notation for the gas constant
The gas constant defined in this article is the universal gas constant, , that applies to any gas. There is also a specific gas constant, which can be denoted as . The specific gas constant is defined as where is the molecular weight.
Unfortunately, many authors in the technical literature sometimes use as the specific gas constant without denoting it as such or stating that it is the specific gas constant. This can and does lead to confusion for many readers.
Reference
- ↑ Molar gas constant Obtained on 16 December, 2007 from the NIST website