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Carbon dioxide
The chemical compound carbon dioxide, or CO2, is an atmospheric gas composed Name Carbon dioxide of one carbon and two oxygen atoms. Chemical CO2 Carbon dioxide results from the Formula combustion of organic matter if Appearance Colourless gas sufficient amounts of oxygen are present. It is also produced by Physical various microorganisms in fermentation Formula weight 44.0 amu and is breathed out by animals. Plants Liquifies under high absorb carbon dioxide during Melting point pressure at 216 K photosynthesis, using both the carbon (-57 ˇC) and the oxygen to construct carbohydrates. It is present in the Boiling point sublimes at 195 K Earth's atmosphere at a low (-78 ˇC) concentration and acts as a greenhouse 1.6 ×103 kg/m3 gas. It is a major component of the carbon cycle. Density (solid) 1.98 kg/m3 (gas at 298 K) Solubility 0.145 g in 100g water Thermochemistry ΔfH0gas -393.52 kJ/mol ΔfH0solid ? kJ/mol S0gas, 1 bar 213.79 J/moláK Chemical and physical properties S0solid ? J/moláK Carbon dioxide is a colorless gas with a weak odor. Its density at 298K is Safety 1.98 kg m-3, about 1.5 times that of May cause nausea, air. The carbon dioxide molecule Ingestion vomiting, GI hemorrhage. O=C=O Asphyxiant (suffocating), contains two double bonds and has a linear shape. It has no electrical Inhalation causes hyperventilation. dipole. As it is fully oxidized, it is Repeated exposure not very reactive and in particular dangerous. not flammable. Skin Dry ice may cause frostbite. Carbon dioxide can be reduced to a liquid and solid form by intense Eyes Can be dangerous. pressure. At standard pressure, it is never liquid: it directly passes More info Hazardous Chemical Database between the gaseous and solid phase at -78ˇC in a process called sublimation. SI units were used where possible. Unless otherwise stated, standard Water will absorb its own volume of conditions were used. carbon dioxide, and more than this under pressure. About 1% of the Disclaimer and references dissolved carbon dioxide turns into carbonic acid, resulting in a slightly acidic taste. The carbonic acid in turn dissociates partly to form bicarbonate and carbonate ions. Uses Carbon dioxide in its solid frozen form it is also known as dry ice. It is used * for cooling * to produce 'dry ice fog' for special effects: when dry ice is put into contact with water, the resulting mixture of CO2 and cold humid air causes condensation and a fog * for cleaning: shooting tiny dry ice pellets at a surface cools the dirt and causes it to pop off Dry ice is produced by compressing CO2 to a liquid form, removing excess heat, and then letting the liquid carbon dioxide expand quickly. This expansion causes a drop in temperature so that some of the CO2 freezes to "snow" which is then compressed. Carbon dioxide extinguishes flames, and some fire extinguishers contain pressured liquid carbon dioxide. Life jackets often contain capsules of pressured liquid carbon dioxide used for quick inflation. Water containing dissolved carbon dioxide is also known as carbonated water or soda water. Carbonated water is contained in many soft drinks and some natural springs. Some beverages, such as beer and sparkling wine contain carbon dioxide as a result of fermentation. Many leavening agents used for baking produce carbon dioxide to cause the dough to rise. Examples are baker's yeast and baking powder. Biology Carbon dioxide is a waste product in organisms that obtain energy from breaking down sugars or fats with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood (where most of it is held in solution) from the body's tissues to the lungs where it is exhaled. Carbon dioxide, when breathed in high concentrations (about 5% by volume), is toxic to humans and other animals. Hemoglobin, the main molecule in red blood cells, can bind both to oxygen and to carbon dioxide. If the CO2 concentration is too high, then all hemoglobin is saturated with carbon dioxide and no oxygen transport takes place (even if plenty of oxygen is in the air). Carbon dioxide and dry ice should therefore only be handled in well ventilated areas. Plants remove carbon dioxide from the atmosphere by photosynthesis, which uses light energy to produce organic plant materials by combining carbon dioxide and water. This releases free oxygen gas. Sometimes carbon dioxide gas is pumped into greenhouses to promote plant growth. Atmosphere The earth's atmosphere contains about 0.037% or 370 ppm CO2 by volume. Due to the greater land area, and therefore greater plant life, in the northern hemisphere as compared to the southern hemisphere, there is an annual fluctuation of about 5 ppm, peaking in May and reaching a minimum in October at the end of the northern hemisphere growing season, when the quantity of biomass on the planet is greatest. Despite its small concentration, CO2 is a very important component of Earth's atmosphere, because it traps infrared radiation and enhances the greenhouse effect of water vapor, thus keeping the Earth from cooling down. The initial carbon dioxide in the atmosphere of the young Earth was produced by volcanic activity; this was necessary for a warm and stable climate conducive to life. Volcanic activity now releases about 130-230 million metric tons (145-255 million short tons) of carbon dioxide each year. Volcanic releases are about 1% the amount which is released by human activities. Atmospheric CO2 has increased about 30 percent since the early 1800s, with an estimated increase of 17 percent since 1958. Burning fossil fuels such as coal and petroleum is the leading cause of increased man-made CO2, deforestation the second major cause. The global warming hypothesis was first recorded in scientific literature near the end of the 19th century. It predicts that increased amounts of CO2 in the atmosphere tend to increase the greenhouse effect and thus contribute to global warming. The size of this effect is still a matter of debate. The widespread opinion that there is currently a warming phase and that the increased carbon dioxide concentration is a major contributor to it has led to international agreements such as the Kyoto Protocol which aim to regulate the release of CO2 into the atmosphere. See also: global warming controversy. Carbon dioxide is the main component of the atmospheres of Mars and Venus. Oceans The Earth's oceans dissolve a major amount of carbon dioxide. The resulting carbonate anions bind to cations present in sea water such as Ca2+ and Mg2+ to form deposits of limestone and dolomite. Most carbon dioxide in the atmosphere eventually undergoes this fate: if all the carbonate rocks in the earth's crust were to be converted back in to carbon dioxide, the resulting carbon dioxide would weigh 40 times as much as the rest of the atmosphere. History Carbon dioxide was first described by the Belgian chemist Jan Baptist van Helmont in the 17th century.
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