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Gas Encyclopedia

The Air Liquide Gas Encyclopedia ensures that you can quickly find full information on more than 135 gas molecules.

Air Liquide and its research teams are making reference content on gases available to students, scientists, professional users, and everyone interested.

Thanks to the Air Liquide Gas Encyclopedia, you will be able to:

  • Find all of the physical properties of gases (the main physical characteristics of molecules in their solid, liquid and gaseous or supercritical states),
  • Calculate the correspondence between the gaseous and liquid phase for a given weight or volume of gas,
  • Calculate the liquid phase density all along the liquid-vapor balance curve for nitrogen, carbon dioxide, argon, hydrogen or oxygen,
  • Download the vapor pressure curve for some gases,
  • View the Safety Datasheets (SDS),
  • Discover the main applications of these gases in industry and healthcare,
  • Check material compatibility.

Using the Encyclopedia

You can run a search by entering a chemical formula, a UN transportation code or by choosing a molecule name from the drop-down menu. Having trouble? Refer to our User Guide.
Gas selection
After selecting a molecule, you can choose the units in which you want displayed numeric values.
Carbon dioxide
Carbon dioxide
CAS Number : 124-38-9
UN1013 (gas); UN2187 (liquid refrigerated); UN1845 (solid)

;Carbonic anhydride; Dry ice;
Carbon dioxide gas is formed from the combination of two elements: carbon and oxygen. It is produced from the combustion of coal or hydrocarbons, the fermentation of liquids and the breathing of humans and animals. Found in small proportions in the atmosphere, it is assimilated by plants which in turn produce oxygen. CO2 gas has a slightly irritating odor, is colorless and heavier than air. It cannot sustain life. It freezes at -78.5 °C to form carbon dioxide snow. In an aqueous solution it forms carbonic acid, which is too unstable to be easily isolated.
Carbon dioxide: 
Main applications
  • Industries

  • Carbon dioxide is used in chemistry for controlling reactor temperatures.
    CO2 is also employed to neutralize alkaline effluents.
    Carbon dioxide is used under supercritical conditions for purifying or dying polymer, animal or vegetal fibers.
  • Carbon dioxide is used for inerting, chemical synthesis, supercritical fluid extraction (SFE), acidification (pH) of wastewater or product transportation at low temperature (-78 °C or -108 °F).
  • CO2 is used in the food business in these main areas:
    - Carbonation of fizzing beverages such as soft drinks, mineral water or beer,
    - Packaging of foodstuffs, its inerting and bacteriostatic properties being used successfully in nitrogen mixtures (Modified Atmosphere Packaging or MAP), to increase the shelf life of many food products (§ ALIGAL™).
    - As cryogenic fluid in chilling or freezing operations or as dry ice for temperature control during the distribution of foodstuffs.
    - Cafein is removal from cafee using supercritical CO2.
  • CO2 produces close-to-physiologic atmospheres for the operation of artificial organs.
    Carbon dioxide is used as a component in a mixture of oxygen or air as respiratory stimulant to promote deep breathing. It is also used for the surgical dilation by intra-abdominal insufflations.
  • Carbon Dioxide is typically used for environment protection:
    - CO2 is used for red fume suppression during scrap and carbon charging, for nitrogen pick-up reduction during EAF tapping and for bottom stirring.
    - In the non ferrous metallurgy, carbon dioxide is used for fume suppression during ladle transfer of matte (Cu/Ni production) or bullion (Zn/Pb production).
    - Small amount of liquid CO2 can be used in recycling of waters from Acid Mine Drainage (AMD).
    - The well known CO2 lasers are feed with some special grades of carbon dioxide (§ LASAL™).
  • Carbon dioxide enables to sharply tune the pH of recycled mechanical or chemical pulps after an alkaline bleaching.
    CO2 can be used in the Tall Oil neutralization and for increasing the performance of paper machines.
  • Carbon dioxide is usually used in waste water treatment, as a cooling medium in environmental testing of electronic devices.
    Carbon dioxide can be used to add conductivity to ultrapure water, for CO2 snow abrasive cleaning of parts or residues on wafers. CO2 can also be used as an environmentally friendly supercritical fluid for removing photoresist from wafers, thus avoid organic solvent use.
  • Injection of carbon dioxide allows to master the pH of liquid effluents. CO2 is an excellent alternative to sulfuric acid for pH balance control.
  •  Other industries 
    Carbon dioxide snow for fire extinguishers;
    pH control and regulation of waste waters, swimming pools,…
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Gas Properties
Molecular Weight
  • Molecular weight  : 44.01 g/mol
Solid phase
  • Melting point (1.013 bar and 0 °C (32 °F)) : -56.57 °C
  • Latent heat of fusion (1,013 bar, at melting point) : 204.93 kJ/kg
  • Solid density  : 1562 kg/m3
Liquid phase
  • Liquid density (at -20 °C (or -4 °F) and 19.7 bar) : 1256.74 kg/m3
  • Liquid/gas equivalent (1.013 bar and 15 °C (per kg of solid)) : 845 vol/vol
  • Boiling point (Sublimation) : -78.45 °C
  • Vapor pressure (at 20 °C or 68 °F) : 57.291 bar
Density & temperature calculation of the liquid phase
Given the pressure (in bar), this module calculates the temperature and the density of the liquid phase on the liquid-gas equilibrium curve
Enter the pressure in bar (between 7 and 26) bar  
Critical point
  • Critical temperature  : 30.98 °C
  • Critical pressure  : 73.77 bar
  • Critical density  : 467.6 kg/m3
Triple point
  • Triple point temperature  : -56.56 °C
  • Triple point pressure  : 5.187 bar
Gaseous phase
  • Gas density (1.013 bar at sublimation point) : 2.813 kg/m3
  • Gas density (1.013 bar and 15 °C (59 °F)) : 1.8714 kg/m3
  • Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 0.99435
  • Specific gravity  : 1.53
  • Specific volume (1.013 bar and 25 °C (77 °F)) : 0.5532 m3/kg
  • Heat capacity at constant pressure (Cp) (1.013 bar and 25 °C (77 °F)) : 0.0374 kJ/(mol.K)
  • Heat capacity at constant volume (Cv) (1.013 bar and 25 °C (77 °F)) : 0.0289 kJ/(mol.K)
  • Ratio of specific heats (Gamma:Cp/Cv) (1.013 bar and 25 °C (77 °F)) : 1.2941
  • Viscosity (1.013 bar and 0 °C (32 °F)) : 1.3711E-04 Poise
  • Thermal conductivity (1.013 bar and 0 °C (32 °F)) : 14.674 mW/(m.K)
  • Solubility in water (1.013 bar and 0 °C (32 °F)) : 1.7163 vol/vol
  • Concentration in air  : 0.04 vol %
Go back to choosing the units
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Vapor Pressure Graph
Vapor Pressure Graph
The vapor pressure curve may be obtained by clicking on the image. On the graph, pressure is in bar or 0.1 MPa, temperature in K or °C. The critical point is indicated by a black spot on the liquid-vapor equilibrium curve.

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Liquid Gas Conversion
Liquid to gas conversion
This module enables a volume (measured at 1 atmosphere and boiling point) or a mass of liquid gas to be converted into a volume or a mass of gas measured at 1 atmosphere and 15 °C.
Data : liquid Phase
Input the volume (m3) or mass (kg)

Gas to liquid conversion
This module enables a volume (measured at 1 atmosphere and 15 °C) or a mass of gas in gaseous phase to be converted into a mass or a volume of liquid (measured at 1 atmosphere and boiling point).
Data : Gas Phase
Input the volume (m3) or mass (kg)

Go back to choosing the units

Safety Data Sheets
Safety Data Sheets (SDS) include information on product ingredients, physical and chemical properties, potential effects on toxicology and ecology, identification of hazards, handling and storage instructions, as well as personnel protection recommendations and information related to transportation requirements, first-aid and emergency processes.


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Major Hazards
  • Major hazard : High Pressure and Inhalation
  • Toxicity (Am. Conf. Of Gov. Ind. Hygienists ACGIH 2000 Edition) : 5000 ppm
  • Flammability limits in air (STP conditions) : Non-flammable
  • Odour : None
  • UN Number : UN1013 (gas); UN2187 (liquid refrigerated); UN1845 (solid)
  • EINECS Number : 204-696-9
  • DOT Label (USA) : NFG
  • DOT Hazard class (USA) : Non flammable Gas
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Material compatibility
Air Liquide has assembled data on the compatibility of gases with materials to assist you in evaluating which products to use for a gas system. Although the information has been compiled from what Air Liquide believes are reliable sources (International Standards: Compatibility of cylinder and valve materials with gas content; Part 1: ISO 11114-1 (Jul 1998), Part 2: ISO 11114-2 (Mar 2001)), it must be used with extreme caution. No raw data such as this can cover all conditions of concentration, temperature, humidity, impurities and aeration. It is therefore recommended that this table is used to choose possible materials and then more extensive investigation and testing is carried out under the specific conditions of use. The collected data mainly concern high pressure applications at ambiant temperature and the safety aspect of material compatibity rather than the quality aspect.
  • Aluminium
  • Brass
  • Copper
  • Ferritic Steels (e.g. Carbon steels)
    Satisfactory but risk of corrosion in presence of CO and/or moisture. Cold brittleness.
  • Stainless Steel
  • Polytetrafluoroethylene (PTFE)
  • Polychlorotrifluoroethylene (PCTFE)
  • Vinylidene polyfluoride (PVDF) (KYNAR)
  • Polyamide (PA) (NYLON)
  • Polypropylene (PP)
  • Buthyl (isobutene - isoprene) rubber (IIR)
    Non recommended, significant swelling.
  • Nitrile rubber (NBR)
    Non recommended, significant swelling and significant loss of mass by extraction or chemical reaction.
  • Chloroprene (CR)
    Non recommended, significant swelling and significant loss of mass by extraction or chemical reaction.
  • Chlorofluorocarbons (FKM) (VITON)
    Non recommended, significant swelling and significant loss of mass by extraction or chemical reaction.
  • Silicon (Q)
    Acceptable but strong rate of permeation.
  • Ethylene - Propylene (EPDM)
    Acceptable but important swelling and significant loss of mass by extraction or chemical reaction.
  • Hydrocarbon based lubricant
  • Fluorocarbon based lubricant
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Selection of the units
You can choose the units in which the values are displayed. By default, SI units are selected.


  • Quantity


  • Mass
    kg lb g
  • Volume
    m3 ft3 l
  • Pressure
    bar psi kPa
  • Temperature
    °C °F K °R
  • Density
    kg/m3 lb/ft3 mol/l (lb-mol)/ft3
  • Enthalpy
    kJ/kg Btu/lb kJ/mol kcal/kg kcal/mol Btu/lb-mol
  • Heat Capacity
    kJ/(mol.K) Btu/(lb.°F) kJ/(kg.K) Btu/(lb-mol.°F) kcal/(kg.K)
    cal/(mol.K) J/(mol.K)
  • Viscosity
    Poise lb/(ft.s) µPa.s Pa.s
  • Thermal Conductivity
    mW/(m.K) Btu.ft/(h.ft2.°F) cal.cm/(h.cm2.°C) W/(m.K)
  • Concentration
    vol % vol ppm vol/vol
  • Solubility
    vol/vol lb/ft3 (lb-mol)/ft3 mol/l g/l
  • Specific volume
    m3/kg ft3/lb l/mol ft3/lb-mol

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