Critical Points for some Substances
Critical points of some common substances like air, argon, helium and more
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At the critical point there is
- no change of state when pressure is increased or if heat is added
At the critical point the liquid and gas phase can't be distinguished and there is no point referring to liquid or gas.
At the critical point the physical properties of the liquid and gaseous states are identical.
For states above the critical point the gas is supercritical.
| Substance | Temperature (K) | Pressure (atm) | Specific Molar Volume (cm3/gmol) | Compressibility Z = Pv/RT |
|---|---|---|---|---|
| Acetylene - C2H2 | 309.5 | 61.6 | 113 | 0.274 |
| Air | 132.63 | 37.36 | 92.35 | |
| Argon - Ar | 150.72 | 47.99 | 75 | 0.291 |
| n-Butane - C4H10 | 425.17 | 37.47 | 255 | 0.274 |
| Carbon Dioxide - CO2 | 304.20 | 72.90 | 94 | 0.275 |
| Carbon Monoxide - CO | 132.91 | 34.529 | 93 | 0.294 |
| Ethane - C2H6 | 305.48 | 48.20 | 148 | 0.285 |
| Ethylene - C2H4 | 283.06 | 50.50 | 124 | 0.270 |
| Helium - He | 5.19 | 2.26 | 58 | 0.308 |
| Hydrogen - H2 | 33.24 | 12.797 | 65 | 0.304 |
| Methane - CH4 | 190.7 | 45.8 | 99 | 0.290 |
| Nitrogen - N2 | 126.2 | 33.54 | 90 | 0.291 |
| Oxygen - O2 | 154.78 | 50.14 | 74 | 0.292 |
| Propane - C3H8 | 370.01 | 42.1 | 200 | 0.277 |
| Sulfur Dioxide - SO2 | 430.7 | 77.8 | 122 | 0.269 |
| Water - H2O | 647.27 | 218.167 | 56 | 0.230 |
Note! - the critical point is not the same as the triple point.
- 1 cm3/gmol = 10-3 liter/mol
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