Gas Constant
The gas constant is a physical constant denoted by R and is expressed in terms of units of energy per temperature increment per mole. It is also known as Ideal gas constant or molar gas constant or universal gas constant. The gas constant value is equivalent to Boltzmann constant but expressed as the pressure-volume product instead of energy per increment of temperature per particle.
Gas Constant Value
In physics, the gas constant is proportionality constant used to relate the energy scale to temperature scale, when one mole of particles at a defined temperature is considered. The ideal gas constant is the combination of Boyle’s law, Avogadro’s number, Charles’s law and Gay-Lussac’s law. Thus, gas constant R value can be given as –
Gas constant R = 8.3144598(48) J⋅mol−1⋅K−1
The digits inside the parentheses are the uncertainty in the measurement of gas constant value.
Gas Constant In Different Units
The gas constant is inversely used in diverse disciplines. Hence it is expressed in many units. Some of the gas constant value in different units are listed below-
Gas Constant Value |
Units |
8.3144598(48) |
J⋅K−1⋅mol−1 |
8.3144598(48)×103 |
amu.m2.s-2.K-1 |
8.3144598(48)×10−2 |
L.bar.K-1.mol-1 |
8.3144598(48) |
m3.Pa.K-1.mol-1 |
62.363577(36) |
L.Torr.K-1.mol-1 |
1.9872036(11)×10−3 |
kcal.K-1.mol-1 |
8.2057338(47)×10−5 |
m3.atm.K-1.mol-1 |
0.082057338(47) |
L.atm.K-1.mol-1 |
R Constant For Atm
The US Standard Atmosphere the R constant for atm is given as
R = 8.31432×103 N⋅m⋅kmol−1⋅K−1.
Specific Gas Constant
The ratio of molar gas constant(R) to the molar mass(M) of the gas mixture is called The specific gas constant. Denoted by Rspecific Mathematically expressed as –
\(R_{specific}= \frac{R}{M}\)
Gas Constant Of Air
The gas constant of air in different units is given in the table mentioned below-
Gas constant of air (Rspecific) |
Units |
287.058 |
J.Kg-1.K-1 |
53.3533 |
ft.lbf.lb-1.0R–1 |
1716.49 |
ft.lbf.slub-1.0R-1 |
The gas constant of air values are based on the mean molar mass of dry air is 28.9645g/mol.
Dimensions
Using the ideal gas equation PV = n RT. The gas constant R can be expressed as-
\(R=\frac{PV}{nT}\)
Where,
- P is the pressure.
- V is the volume,
- n is the number of moles of the given substance
- T is the temperature.
Thus, writing pressure as force per unit area we can derive the dimensional expression for R as-
\(R=\frac{\left ( \frac{force}{area} \right )\times volume}{amount\;\times temperature}\)
Area and Volume can be expressed in terms of length as volume=(length)3 and area = (length)2
Thus we get-
\(R=\frac{\left ( \frac{force}{length^{2}} \right )\times \left ( length \right )^{3}}{amount\;\times temperature}=\frac{force\;\times\; length}{amount\;\times \;temperature}\)
Since force times length is work we get-
\(R=\frac{work}{amount\;\times \;temperature}\)
Thus gas constant can be interpreted as work per degree per mole.