page_title: Carbon dioxide
section_title: Physical properties
hierarchical_section_title: Carbon dioxide / Chemical and physical properties / Physical properties
caption_attribution_description: English: Small pellets of dry ice sublimating in air. The pellets are approx 0.5 - 1.0cm in diameter. Français&#160;: Petites pastilles de glace sèche se sublimant dans l'air. Les pastilles ont un diamètre d'environ 0,5 à 1,0 cm.
context_page_description: Carbon dioxide is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide consists 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% by volume, having risen from pre-industrial levels of 280 ppm. 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 is odorless at normally encountered concentrations, but at high concentrations, it has a sharp and acidic odor. At such concentrations it generates the taste of soda water in the mouth.
  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.
context_section_description: Carbon dioxide is colorless. At low concentrations the gas is odorless; however, at sufficiently-high concentrations, it has a sharp, acidic odor. At standard temperature and pressure, the density of carbon dioxide is around 1.98 kg/m³, about 1.67 times that of air.
  Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520 kPa). At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below −78.5 °C (−109.3 °F; 194.7 K) and the solid sublimes directly to a gas above −78.5 °C. In its solid state, carbon dioxide is commonly called dry ice.
  Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 5.1 bar (517 kPa) at 217 K (see phase diagram). The critical point is 7.38 MPa at 31.1 °C. Another form of solid carbon dioxide observed at high pressure is an amorphous glass-like solid. This form of glass, called carbonia, is produced by supercooling heated CO
  2 at extreme pressure (40–48 GPa or about 400,000 atmospheres) in a diamond anvil. This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like silicon (silica glass) and germanium dioxide. Unlike silica and germania glasses, however, carbonia glass is not stable at normal pressures and reverts to gas when pressure is released.
  At temperatures and pressures above the critical point, carbon dioxide behaves as a supercritical fluid known as supercritical carbon dioxide.  In this state it is starting (as of 2018) to be used for power generation.
caption: Pellets of "dry ice", a common form of solid carbon dioxide
exif: {}