The constant $R$ in the ideal gas equation of state may have different values according to the unit system in use. For example
| $R$ | Units |
|---|---|
| SI units | |
| 8.314 | $J\,K^{−1}\,mol^{−1}$ |
| 8.314 | $m^3\,Pa\,K^{−1}\,mol^{−1}$ |
| 8.314 | $kg\,m^2\,s^{-2}\,K^{−1}\,mol^{−1}$ |
| Other units | |
| 8314.462 | $L\,Pa\,K^{−1}\,mol^{−1}$ |
| 8.314 | $L\,kPa\,K^{−1}\,mol^{−1}$ |
| $8.314\times10^{-2}$ | $L\,bar\,K^{−1}\,mol^{−1}$ |
| $8.314\times10^{7}$ | $erg\,K^{−1}\,mol^{−1}$ |
| $7.302\times10^{-1}$ | $atm\,ft^3\,lb_{mol}^{−1}\,R^{−1}$ |
| 10.731 | $psi\,ft^3\,lb_{mol}^{−1}\,R^{−1}$ |
| 1.986 | $BTU\,lb_{mol}^{−1}\,R^{−1}$ |
| 297.031 | $inH_2O\,ft^3\,lb_{mol}^{−1}\,R^{−1}$ |
| 554.984 | $torr\,ft^3\,lb_{mol}^{−1}\,R^{−1}$ |
| $8.206\times10^{-2}$ | $L\,atm\,K^{−1}\,mol^{−1}$ |
| 62.363 | $L\,torr\,K^{−1}\,mol^{−1}$ |
| 1.987 | $cal\,K^{−1}\,mol^{−1}$ |
| $8.206\times10^{-5}$ | $m^3\,atm\,K^{−1}\,mol^{−1}$ |
However, as you may imagine if a gas in question has an idealized behavior then the constant $R$ may apply. A gas behaves as an ideal gas under certain conditions of pressure, $P=0$, and temperature so that the following equation of state applies
$PV=nRT$
One way to check for the constant $R$ for any given gas is in a plot of $PV/nT$ versus $P$ which should be a straight line. Also, when this line cuts the vertical axis ($PV/nT$) at $P=0$ you should read any of the values of the table above (according to the units you were using).
Other stuff of interest
- LE01 - AC and DC voltage measurement and continuity test
- LE 02 - Start and stop push button installation 24V DC
- What is an Equation of State
- Minor losses - Formulas
- What is a process variable?
- What are the most important process variables?
- Time dependence of process variables
- A list of process variables
Ildebrando.
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