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# Critical Temperatures and Pressures for some Common Substances

## Critical temperatures and pressures for some common substances like air, alcohol, ether, oxygen and more.

Gases can be converted to liquids by compressing the gas at a suitable temperature. However, they become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase. At the critical temperature they cannot longer be liquified.

• Critical Temperature: The temperature which above, a substance can not exist as a liquid, no matter how much pressure is applied. Every substance has a critical temperature.
• Critical Pressure: The pressure required to liquify a substance vapor at its critical temperature
• Critical point: The end point of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist. At higher temperatures, the gas cannot be liquefied by pressure alone. At the critical point, defined by the critical temperature Tc and the critical pressure pc, phase boundaries vanish.
• Triple point:  The temperature and pressure at which the three phases (gas, liquid, and solid) of a substance coexist in thermodynamic equilibrium.

The table below shows critical temperature and pressure for some common substances, together with boiling temperature.

See Triple point for listing of triple point values for common substances.

SubstanceCritical temperatureCritical pressureBoiling temperature
(1 atm)
[°F][°C][psi], [lb/in2]

[bar][°F][°C]
Air -220.94 -140.52 549.08 37.858 - -
Ammonia (NH3) 270 132.4 1636 112.8 -27.4 -33
Argon -188 -122 705.6 48.7 -302.5 -185.8
Butane 305.6 152 550.4 38 32 0
Carbon-dioxide (CO2) 87.8 31.2 1071.6 73.8 -110 -79
Carbon-monoxide (CO) -220.5 -140.3 507.5 35 -310 -190
Chlorine 291 144 1118.7 77.1 -29.3 -34
Decane 653 345 301.7 20.8 345 174
Dowtherm A 465 32.1
Ethane 90.0 32.2 708 48.9 -127.4 -88.5
Ethanol (alcohol) 467 242 914 63 173 78.4
Ethylether 381 194 522 36 94.2 34.6
Ethylene 48.9 9.4 735 50.7 -272.6 -169.2
Fluorine -200 -129 808.5 55.8 -307 -188
Helium -456 -271 33.2 2.3 -452 -269
Hydrogen (H) -400 -240 188.2 13.0 -423 -253
Hydrogen Chloride 125 51.6 1198 82.7 -121.1 -85.1
Isobutane 274 135 529.2 36.5 10.9 -11.7
Isobutylene 293 145 580 40.0 19.6 -6.9
Isononane 590 310 335.1 23.1 303 151
Methane -117 -82.6 673.3 46.5 -259 -162
Nitrogen (N) -232.6 -147 492.4 34.0 -321 -195
Nitrous Oxide (N2O) 97.4 36.4 1047.6 72.3 -127 -88.5
Oxygen (O2) -181.5 -118.6 732 50.5 -297 -183
Phosgene 823.2 56.8 46.9 8.3
Propane 206.1 96.7 617.4 42.6 -44 -42
Propylbenzene 689 365 464.2 32 319 159
Propylene 198 92.4 670.3 46.3 -54 -48
Refrigerants
Undecane 691 366 287.2 19.8 385 196
Water 705 374 3206.2 220.5 212 100

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