Carbon Dioxide CO2

Carbon dioxide (<a href="http://en.wikipedia.org/wiki/Chemical_formula" title="Chemical formula" >chemical formula</a> CO2) is a naturally occurring <a href="http://en.wikipedia.org/wiki/Chemical_compound" title="Chemical compound" >chemical compound</a> composed of two <a href="http://en.wikipedia.org/wiki/Oxygen" title="Oxygen" >oxygen</a> <a href="http://en.wikipedia.org/wiki/Atom" title="Atom" >atoms</a> <a href="http://en.wikipedia.org/wiki/Covalent_bond" title="Covalent bond" >covalently bonded</a> to a single <a href="http://en.wikipedia.org/wiki/Carbon" title="Carbon" >carbon</a> atom. It is a <a href="http://en.wikipedia.org/wiki/Gas" title="Gas" >gas</a> at <a href="http://en.wikipedia.org/wiki/Standard_temperature_and_pressure" title="Standard temperature and pressure" class="mw-redirect" >standard temperature and pressure</a> and exists in <a href="http://en.wikipedia.org/wiki/Earth%27s_atmosphere" title="Earth's atmosphere" class="mw-redirect" >Earth's atmosphere</a> in this state, as a <a href="http://en.wikipedia.org/wiki/Trace_gas" title="Trace gas" >trace gas</a> at a concentration of 0.039% by volume.

As part of the <a href="http://en.wikipedia.org/wiki/Carbon_cycle" title="Carbon cycle" >carbon cycle</a> known as <a href="http://en.wikipedia.org/wiki/Photosynthesis" title="Photosynthesis" >photosynthesis</a>, <a href="http://en.wikipedia.org/wiki/Plant" title="Plant" >plants</a>,<a href="http://en.wikipedia.org/wiki/Algae" title="Algae" >algae</a>, and <a href="http://en.wikipedia.org/wiki/Cyanobacteria" title="Cyanobacteria" >cyanobacteria</a> absorb carbon dioxide, <a href="http://en.wikipedia.org/wiki/Light" title="Light" >light</a>, and <a href="http://en.wikipedia.org/wiki/Water" title="Water" >water</a> to produce <a href="http://en.wikipedia.org/wiki/Carbohydrate" title="Carbohydrate" >carbohydrate</a> <a href="http://en.wikipedia.org/wiki/Energy" title="Energy" >energy</a> for themselves and <a href="http://en.wikipedia.org/wiki/Oxygen" title="Oxygen" >oxygen</a> as a waste product.

But in darkness photosynthesis cannot occur, and during the resultant <a href="http://en.wikipedia.org/wiki/Cellular_respiration" title="Cellular respiration" >respiration</a> small amounts of

carbon dioxide are produced.<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-1" >[2]</a>

Carbon dioxide is also produced by <a href="http://en.wikipedia.org/wiki/Combustion" title="Combustion" >combustion</a> of coal or <a href="http://en.wikipedia.org/wiki/Hydrocarbon" title="Hydrocarbon" >hydrocarbons</a>, the fermentation of liquids and the breathing of humans and animals. In addition it is emitted from <a href="http://en.wikipedia.org/wiki/Volcano" title="Volcano" >volcanoes</a>, <a href="http://en.wikipedia.org/wiki/Hot_spring" title="Hot spring" >hot springs</a>, <a href="http://en.wikipedia.org/wiki/Geyser" title="Geyser" >geysers</a> and other places where the earth’s crust is thin; and is freed from <a href="http://en.wikipedia.org/wiki/Carbonate_rock" title="Carbonate rock" >carbonate rocks</a>by <a href="http://en.wikipedia.org/wiki/Dissolution" title="Dissolution" >dissolution</a>. CO2 is also found in lakes at depth under the sea, and commingled with oil and gas deposits.<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-2" >[3]</a>

<h3 >Foods</h3>

Carbon dioxide is a <a href="http://en.wikipedia.org/wiki/Food_additive" title="Food additive" >food additive</a> used as a propellant and acidity regulator in the food industry. It is approved for usage in the EU<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-15" >[16]</a> (listed as <a href="http://en.wikipedia.org/wiki/E_number" title="E number" >E number</a> E290), USA<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-16" >[17]</a>and Australia and New Zealand<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-17" >[18]</a> (listed by its INS number 290).

A candy called <a href="http://en.wikipedia.org/wiki/Pop_Rocks" title="Pop Rocks" >Pop Rocks</a> is pressurized with carbon dioxide gas at about 40 bar (580 psi). When placed in the mouth, it dissolves (just like other hard candy) and releases the gas bubbles with an audible pop.

<a href="http://en.wikipedia.org/wiki/Leavening_agent" title="Leavening agent" >Leavening agents</a> cause dough to rise by producing carbon dioxide. <a href="http://en.wikipedia.org/wiki/Baker%27s_yeast" title="Baker's yeast" >Baker's yeast</a> produces carbon dioxide by fermentation of sugars within the dough, while chemical leaveners such as <a href="http://en.wikipedia.org/wiki/Baking_powder" title="Baking powder" >baking powder</a> and <a href="http://en.wikipedia.org/wiki/Baking_soda" title="Baking soda" class="mw-redirect" >baking soda</a> release carbon dioxide when heated or if exposed to <a href="http://en.wikipedia.org/wiki/Acid" title="Acid" >acids</a>.

<h4 >Beverages</h4>

Carbon dioxide is used to produce <a href="http://en.wikipedia.org/wiki/Carbonation" title="Carbonation" >carbonated</a> <a href="http://en.wikipedia.org/wiki/Soft_drinks" title="Soft drinks" class="mw-redirect" >soft drinks</a> and <a href="http://en.wikipedia.org/wiki/Soda_water" title="Soda water" class="mw-redirect" >soda water</a>. Traditionally, the carbonation

in beer and sparkling wine came about through natural fermentation, but many manufacturers carbonate these drinks with carbon dioxide recovered from the fermentation process. In the case of bottled and kegged beer, recycled carbon dioxide carbonation is the most common method used. With the exception of British <a href="http://en.wikipedia.org/wiki/Real_Ale" title="Real Ale" class="mw-redirect" >Real Ale</a>, draught beer is usually transferred from kegs in a cold room or cellar to dispensing taps on the bar using pressurized carbon dioxide, sometimes mixed with nitrogen.

<h4 >Wine making</h4>

Carbon dioxide in the form of <a href="http://en.wikipedia.org/wiki/Dry_ice" title="Dry ice" >dry ice</a> is often used in the <a href="http://en.wikipedia.org/wiki/Wine_making" title="Wine making" class="mw-redirect" >wine making</a> process to cool down bunches of<a href="http://en.wikipedia.org/wiki/Grape" title="Grape" >grapes</a> quickly after picking to help prevent spontaneous <a href="http://en.wikipedia.org/wiki/Fermentation(wine)" title="Fermentation (wine)" >fermentation</a> by wild <a href="http://en.wikipedia.org/wiki/Yeast(wine)" title="Yeast (wine)" class="mw-redirect" >yeast</a>. The main advantage of using dry ice over regular water ice is that it cools the grapes without adding any additional water that may decrease the <a href="http://en.wikipedia.org/wiki/Sugar" title="Sugar" >sugar</a> concentration in the <a href="http://en.wikipedia.org/wiki/Grape_must" title="Grape must" class="mw-redirect" >grape must</a>, and therefore also decrease the <a href="http://en.wikipedia.org/wiki/Alcohol" title="Alcohol" >alcohol</a> concentration in the finished wine.

Dry ice is also used during the <a href="http://en.wikipedia.org/w/index.php?title=Cold_soak&action=edit&redlink=1" class="new" title="Cold soak (page does not exist)" >cold soak</a> phase of the wine making process to keep grapes cool. The carbon dioxide gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is heavier than air. The settled carbon dioxide gas creates a hypoxic environment which helps to prevent bacteria from growing on the grapes until it is time to start the fermentation with the desired strain of yeast.

Carbon dioxide is also used to create a hypoxic environment for <a href="http://en.wikipedia.org/wiki/Carbonic_maceration" title="Carbonic maceration" >carbonic maceration</a>, the process used to produce <a href="http://en.wikipedia.org/wiki/Beaujolais" title="Beaujolais" class="mw-redirect" >Beaujolais</a> wine.

Carbon dioxide is sometimes used to top up wine bottles or other <a href="http://en.wikipedia.org/wiki/Storage_(wine)" title="Storage (wine)" class="mw-redirect" >storage</a> vessels such as barrels to

prevent oxidation, though it has the problem that it can dissolve into the wine, making a previously still wine slightly fizzy. For this reason, other gases such as <a href="http://en.wikipedia.org/wiki/Nitrogen" title="Nitrogen" >nitrogen</a> or <a href="http://en.wikipedia.org/wiki/Argon" title="Argon" >argon</a> are preferred for this process by professional wine makers.

The environmental effects of carbon dioxide are of significant interest. In the earth's atmosphere, it 

acts as a <a href="http://en.wikipedia.org/wiki/Greenhouse_gas" title="Greenhouse gas" >greenhouse gas</a> which is believed to play a major role in <a href="http://en.wikipedia.org/wiki/Global_warming" title="Global warming" >global warming</a> and <a href="http://en.wikipedia.org/wiki/Anthropogenic" title="Anthropogenic" class="mw-redirect" >anthropogenic</a> <a href="http://en.wikipedia.org/wiki/Climate_change" title="Climate change" >climate change</a>. Also a major source of <a href="http://en.wikipedia.org/wiki/Ocean_acidification" title="Ocean acidification" >ocean acidification</a> is CO2 which dissolves in

water forming <a href="http://en.wikipedia.org/wiki/Carbonic_acid" title="Carbonic acid" >carbonic acid</a>,<a href="http://en.wikipedia.org/wiki/Carbon_dioxide#cite_note-3" >[4]</a> which is a <a href="http://en.wikipedia.org/wiki/Acid_strength" title="Acid strength" >weak acid</a>, because CO2 molecule ionization in water is incomplete.

Carbon Dioxide CO2

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