Editing Carbon dioxide (section)

=== Biological processes ===
Carbon dioxide is a by-product of the [[Fermentation (biochemistry)|fermentation]] of sugar in the [[brewing]] of [[beer]], [[whisky]] and other [[alcoholic beverage]]s and in the production of [[bioethanol]]. [[Yeast]] metabolizes sugar to produce {{CO2}} and [[ethanol]], also known as alcohol, as follows:
:{{chem2|C6H12O6 -> 2 CO2 + 2 CH3CH2OH}}

All [[cellular respiration|aerobic]] organisms produce {{CO2}} when they oxidize [[carbohydrate]]s, [[fatty acid]]s, and [[protein]]s. The large number of reactions involved are exceedingly complex and not described easily. Refer to [[cellular respiration]], [[anaerobic respiration]] and [[photosynthesis]]. The equation for the respiration of glucose and other [[monosaccharide]]s is:
:{{chem2|C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O}}

[[Anaerobic organisms]] decompose organic material producing methane and carbon dioxide together with traces of other compounds.<ref>{{cite web |date=11 January 2017 |title=Collecting and using biogas from landfills |url=http://www.eia.gov/Energyexplained/?page=biomass_biogas |url-status=live |archive-url=https://web.archive.org/web/20180711073415/https://www.eia.gov/Energyexplained/?page=biomass_biogas |archive-date=11 July 2018 |access-date=22 November 2015 |publisher=U.S. Energy Information Administration}}</ref> Regardless of the type of organic material, the production of gases follows well defined [[chemical kinetics|kinetic pattern]]. Carbon dioxide comprises about 40–45% of the gas that emanates from decomposition in landfills (termed "[[landfill gas]]"). Most of the remaining 50–55% is methane.<ref>{{cite web |date=January 2000 |title=Facts About Landfill Gas |url=http://www.dem.ri.gov/programs/benviron/waste/central/lfgfact.pdf |url-status=live |archive-url=https://web.archive.org/web/20150923213448/http://www.dem.ri.gov/programs/benviron/waste/central/lfgfact.pdf |archive-date=23 September 2015 |access-date=4 September 2015 |publisher=U.S. Environmental Protection Agency}}</ref>

==== Combustion ====
The [[combustion]] of all [[carbon-based fuel]]s, such as [[methane]] ([[natural gas]]), petroleum distillates ([[gasoline]], [[Diesel fuel|diesel]], [[kerosene]], [[propane]]), coal, wood and generic organic matter produces carbon dioxide and, except in the case of pure carbon, water. As an example, the chemical reaction between methane and [[oxygen]]:
:{{chem2|CH4 + 2 O2 -> CO2 + 2 H2O}}

[[Iron]] is reduced from its oxides with [[coke (fuel)|coke]] in a [[blast furnace]], producing [[pig iron]] and carbon dioxide:<ref>
{{Cite book | vauthors = Strassburger J | title = Blast Furnace Theory and Practice | publisher = American Institute of Mining, Metallurgical, and Petroleum Engineers | place = New York | year = 1969 | isbn = 978-0-677-10420-1}}</ref>
:{{chem2|Fe2O3 + 3 CO -> 3 CO2 + 2 Fe}}

==== By-product from hydrogen production ====
Carbon dioxide is a byproduct of the industrial production of hydrogen by [[steam reforming]] and the [[water gas shift reaction]] in [[ammonia production]]. These processes begin with the reaction of water and natural gas (mainly methane).<ref>{{cite book |doi=10.1002/14356007.a05_165|chapter=Carbon Dioxide|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2000| vauthors = Topham S |isbn=3527306730}}</ref>

==== Thermal decomposition of limestone ====
It is produced by thermal decomposition of limestone, {{chem2|CaCO3}} by heating ([[calcining]]) at about {{convert|850|C}}, in the manufacture of [[Calcium oxide|quicklime]] ([[calcium oxide]], CaO), a compound that has many industrial uses:
:{{chem2|CaCO3 -> CaO + CO2}}

Acids liberate {{CO2}} from most metal carbonates. Consequently, it may be obtained directly from natural carbon dioxide [[spring (hydrosphere)|springs]], where it is produced by the action of acidified water on [[limestone]] or [[Dolomite (mineral)|dolomite]]. The reaction between [[hydrochloric acid]] and calcium carbonate (limestone or chalk) is shown below:
:{{chem2|CaCO3 + 2 HCl -> CaCl2 + H2CO3}}

The [[carbonic acid]] ({{chem2|H2CO3}}) then decomposes to water and {{CO2}}:
:{{chem2|H2CO3 -> CO2 + H2O}}

Such reactions are accompanied by foaming or bubbling, or both, as the gas is released. They have widespread uses in industry because they can be used to neutralize waste acid streams.