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[[Image:CO2phase.jpg|thumb|right|300px|[[Phase diagram]] for CO<sub>2</sub>]]
[[Image:CO2phase.jpg|thumb|right|300px|[[Phase diagram]] for CO<sub>2</sub>]]
'''Carbon dioxide''' in an odorless, colorless [[gas]] formed by the [[oxidation]] of [[hydrocarbon]]s, both naturally, in animals, and artificially, as fuel<ref>If not enough oxygen is present, [[carbon monoxide]] will also be produced, in a process called "incomplete combustion".</ref>. It is one of the human body's major waste products, being excreted through exhalation.
'''Carbon dioxide''' (CO<sub>2</sub>) is an odorless, colorless [[gas]] formed by the [[oxidation]] of [[hydrocarbon]]s, both naturally, in animals, and artificially, as fuel<ref>If not enough oxygen is present, [[carbon monoxide]] will also be produced, in a process called [[incomplete combustion]].</ref>. It is one of the human body's major waste products, being excreted through exhalation.
It is used by plants in the process of [[photosynthesis]] to create complex carbohydrates (cellulose and sugars), using water and the energy from sunlight. The waste product in this process is [[oxygen]].
It is used by plants in the process of [[photosynthesis]] to create complex carbohydrates ([[cellulose]] and [[sugar]]s), using water and the energy from sunlight. The waste product in this process is [[oxygen]].
At room temperature and atmospheric [[pressure]], carbon dioxide is a gas. It becomes solid at -78 ºC at standard atmospheric pressure, forming dry ice. When it thaws, it turns directly into a gas again (called [[sublimation]]). <ref>"Dry ice is frozen carbon dioxide. A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C). Dry ice also has the very nice feature of sublimation -- as it breaks down, it turns directly into carbon dioxide gas rather than a liquid." [http://www.howstuffworks.com/question264.htm How Stuff Works] </ref> This can be seen from the phase diagram to the right, where at 1 atmosphere of pressure, there is no liquid state separating the solid and gas as temperature rises.
At room temperature and atmospheric [[pressure]], it is a gas. It becomes solid at -78 ºC at standard atmospheric pressure, forming dry ice. When it thaws, it turns directly into a gas again (see [[sublimation]]). <ref>"Dry ice is frozen carbon dioxide. A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C). Dry ice also has the very nice feature of sublimation -- as it breaks down, it turns directly into carbon dioxide gas rather than a liquid." [http://www.howstuffworks.com/question264.htm How Stuff Works] </ref> This can be seen from the phase diagram to the right, where at 1 atmosphere of pressure, there is no liquid state separating the solid and gas as temperature rises.
CO<sub>2</sub> is one of the so-called [[greenhouse gas]]es. Heat-trapping by CO<sub>2</sub> has been observed on [[Earth]] and [[Venus]]. The extent of its role in the current increase in average global temperatures is a topic of active political, though not scientific, debate.
CO<sub>2</sub> is one of the so-called [[greenhouse gas]]es. Heat-trapping by CO<sub>2</sub> has been observed on [[Earth]] and [[Venus]]. The extent of its role in the current increase in average global temperatures is a topic of active political, though not scientific, debate.
[[Category: Chemistry]]
[[Category: Chemistry]]
[[Category: Chemical Compounds]]