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Engineering ToolBox > Critical Points some common Substances
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/gmole) | Compressibility Z = Pv/RT |
| Acetylene - C2H2 | 309.5 | 61.6 | 113 | 0.274 |
| Air | 132.41 | 37.25 | 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 |