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# Critical Temperatures and Pressures for some Common Substances

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.

Critical Temperatures and Pressures 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

## Related Topics

### • Gases and Compressed Air

Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.

### • Thermodynamics

Work, heat and energy systems.

## Related Documents

### Acetone - Thermophysical Properties

Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.

### Ammonia - Dynamic and Kinematic Viscosity vs. Temperature and Pressure

Online calculator, figures and tables showing dynamic (absolute) and kinematic viscosity of gasous and liquid ammonia at temperatures ranging from -73 to 425°C (-100 to 800°F) at pressure ranging from 1 to 1000 bara (14.5 - 14500 psia) - SI and Imperial Units.

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Figures and tables showing how the properties of liquid and gaseous ammonia changes along the boiling/condensation curve (temperature and pressure between triple point and critical point conditions). An ammonia phase diagram are included.

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Online calculator, figures and tables showing specific heat, CP and CV, of gasous and liquid ammonia at temperatures ranging from -73 to 425°C (-100 to 800°F) at pressure ranging from 1 to 100 bara (14.5 - 1450 psia) - SI and Imperial Units.

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Chemical, Physical and Thermal Properties of Ammonia. Phase diagram included.

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### Benzene - Thermophysical properties

Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.

### Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

### Heavy Water - Thermophysical Properties

Thermodynamic properties of heavy water (D2O) like density, melting temperature, boiling temperature, latent heat of fusion, latent heat of evaporation, critical temperature and more.

### Helium - Thermophysical Properties

Chemical, Physical and Thermal Properties of Helium - He.

### Hydrogen - Thermophysical Properties

Chemical, Physical and Thermal Properties of Hydrogen - H2.

### Liquid Ammonia - Thermal Properties at Saturation Pressure

Density, specific heat, thermal conductivity, viscosity and Prandtls no. of liquid ammonia at saturation pressure.

### Liquids - Critical Pressure Ratios

Critical pressure ratios for water and other liquids.

### Non-ideal gas - Van der Waal's Equation and Constants

The van der Waals constants for more than 200 gases used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles.

### Oxygen - Thermophysical properties

Chemical, Physical and Thermal Properties of Oxygen - O2.

### The Ideal Gas Law

The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.

### Total and Partial Pressure - Dalton's Law of Partial Pressures

How to calculate total pressure and partial pressures for gas mixtures from Ideal Gas Law.

### Triple Points Substances

Triple points for common substances.

### Water vs. Steam - Critical and Triple Points

Critical point is where vapor and liquid are indistinguishable and triple point is where ice, water and vapor coexist in thermodynamic equilibrium.

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