Carbon dioxide

Carbon dioxide
Ball-and-stick model of carbon dioxide
Space-filling model of carbon dioxide
Names
Other names
  • Carbonic acid gas
  • Carbonic anhydride
  • Carbonic dioxide
  • Carbon(IV) oxide
  • R-744 (refrigerant)
  • R744 (refrigerant alternative spelling)
  • Dry ice (solid phase)
Identifiers
3D model (JSmol)
3DMet
1900390
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.271
EC Number
  • 204-696-9
E number E290 (preservatives)
989
KEGG
MeSH Carbon+dioxide
RTECS number
  • FF6400000
UNII
UN number 1013 (gas), 1845 (solid)
  • InChI=1S/CO2/c2-1-3 Y
    Key: CURLTUGMZLYLDI-UHFFFAOYSA-N Y
  • InChI=1/CO2/c2-1-3
    Key: CURLTUGMZLYLDI-UHFFFAOYAO
  • O=C=O
  • C(=O)=O
Properties
CO2
Molar mass 44.009 g·mol−1
Appearance Colorless gas
Odor
  • Low concentrations: none
  • High concentrations: sharp; acidic[1]
Density
  • 1562 kg/m3 (solid at 1 atm (100 kPa) and −78.5 °C (−109.3 °F))
  • 1101 kg/m3 (liquid at saturation −37 °C (−35 °F))
  • 1.977 kg/m3 (gas at 1 atm (100 kPa) and 0 °C (32 °F))
Critical point (T, P) 304.128(15) K[2] (30.978(15) °C), 7.3773(30) MPa[3] (72.808(30) atm)
194.6855(30) K (−78.4645(30) °C) at 1 atm (0.101325 MPa)
1.45 g/L at 25 °C (77 °F), 100 kPa (0.99 atm)
Vapor pressure 5.7292(30) MPa, 56.54(30) atm (20 °C (293.15 K))
Acidity (pKa) 6.35, 10.33
−20.5·10−6 cm3/mol
Thermal conductivity 0.01662 W·m−1·K−1 (300 K (27 °C; 80 °F))[4]
1.00045
Viscosity
  • 14.90 μPa·s at 25 °C (298 K)[5]
  • 70 μPa·s at −78.5 °C (194.7 K)
0 D
Structure
Trigonal
Linear
Thermochemistry
37.135 J/K·mol
214 J·mol−1·K−1
−393.5 kJ·mol−1
Pharmacology
V03AN02 (WHO)
Hazards
Safety data sheet See: data page
Sigma-Aldrich
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
90,000 ppm (human, 5 min)[8]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5000 ppm (9000 mg/m3)[9]
REL (Recommended)
TWA 5000 ppm (9000 mg/m3), ST 30,000 ppm (54,000 mg/m3)[9]
IDLH (Immediate danger)
40,000 ppm[9]
Related compounds
Other anions
Other cations
Related carbon oxides
Related compounds
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solidliquidgas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Carbon dioxide (chemical formula CO
2
) is an acidic colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas. The current concentration is about 0.04% (412 ppm) by volume, having risen from pre-industrial levels of 280 ppm.[10][11] Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, ice caps, glaciers and seawater. It is present in deposits of petroleum and natural gas. Carbon dioxide has a sharp and acidic odor and generates the taste of soda water in the mouth.[12] However, at normally encountered concentrations it is odorless.[1]

As the source of available carbon in the carbon cycle, atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena. Plants, algae and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water in a process called photosynthesis, which produces oxygen as a waste product.[13] In turn, oxygen is consumed and CO2 is released as waste by all aerobic organisms when they metabolize organic compounds to produce energy by respiration.[14] Since plants require CO2 for photosynthesis, and humans and animals depend on plants for food, CO2 is necessary for the survival of life on earth.

It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals, including humans. Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread, beer and wine making. It is produced by combustion of wood, peat and other organic materials and fossil fuels such as coal, petroleum and natural gas. It is an unwanted byproduct in many large scale oxidation processes, for example, in the production of acrylic acid (over 5 million tons/year).[15][16][17]

It is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, as a chemical feedstock and as a supercritical fluid solvent in decaffeination of coffee and supercritical drying.[18] It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence. The frozen solid form of CO2, known as dry ice, is used as a refrigerant and as an abrasive in dry-ice blasting. It is a feedstock for the synthesis of fuels and chemicals.[19][20][21][22]

Carbon dioxide is the most significant long-lived greenhouse gas in Earth's atmosphere. Since the Industrial Revolution anthropogenic emissions – primarily from use of fossil fuels and deforestation – have rapidly increased its concentration in the atmosphere, leading to global warming. Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid.[23]