Definition
Carbon dioxide (CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom.
Basics
Carbon dioxide (CO2) is a gas. It is made of one carbon and two oxygen atoms. We make carbon dioxide when we breathe out. Also, every time something organic is burnt (or a fire is made), it makes carbon dioxide. Plants use carbon dioxide to make food. This gas can also kill and harm many living things.
The big problem with carbon dioxide is that it counts as one of the greenhouse gases. Such gases change the climate and weather on our planet Earth. Overall, this climate change causes global warming, but it can also make winters much longer and colder in some areas.
Dry ice, or solid carbon dioxide, is the solid state of CO2 gas below -109.3 °F (-78.5 °C). Dry ice does not occur naturally on earth but is man made. It is colorless. Common uses include, but are not limited to: carbonating drinks, killing gophers, and freezing warts. The vapor of dry ice causes suffocation and eventually, death. Caution and professional assistance is recommended whenever dry ice is in use.
It will not melt from a solid to a liquid but instead changes directly from a solid to a gas. This is called sublimation. It will change directly from a solid to a gas at any temperature higher than extremely cold temperatures. Dry ice sublimes at normal air temperature. Dry ice exposed to normal air gives off carbon dioxide gas that is odourless and colourless.
The gas is so cold that when it mixes with air it cools the water vapour in the air to fog, which looks like a thick white smoke. It is often used in the theatre to create the appearance of fog or smoke.
Topics of Interest
Carbon dioxide (chemical formula CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas being only 0.038% of the atmosphere.
Carbon dioxide is used by plants during photosynthesis to make sugars, which may either be consumed in respiration or used as the raw material to produce other organic compounds needed for plant growth and development. It is produced during respiration by plants, and by all animals, fungi and microorganisms that depend either directly or indirectly on plants for food. It is thus a major component of the carbon cycle. Carbon dioxide is generated as a by-product of the combustion of fossil fuels or the burning of vegetable matter, among other chemical processes. Small amounts of carbon dioxide are emitted from volcanoes and other geothermal processes such as hot springs and geysers and by the dissolution of carbonates in crustal rocks
As of March 2009, carbon dioxide in the Earth's atmosphere is at a concentration of 387 ppm by volume. Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Carbon dioxide is a greenhouse gas as it transmits visible light but absorbs strongly in the infrared and near-infrared.
Carbon dioxide has no liquid state at pressures below 5.1 atmospheres. At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below −78 °C (−108.4 °F; 195.1 K) and the solid sublimes directly to a gas above −78 °C. In its solid state, carbon dioxide is commonly called dry ice.
CO2 is an acidic oxide: an aqueous solution turns litmus from blue to pink. It is the anhydride of carbonic acid, an acid which is unstable and is known to exist only in aqueous solution. In organisms carbonic acid production is catalysed by the enzyme, carbonic anhydrase.
CO2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy. Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.
History: Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the seventeenth century, the Flemish chemist Jan Baptist van Helmont observed that when he burned charcoal in a closed vessel, the mass of the resulting ash was much less than that of the original charcoal. His interpretation was that the rest of the charcoal had been transmuted into an invisible substance he termed a "gas" or "wild spirit" (spiritus sylvestre).
The properties of carbon dioxide were studied more thoroughly in the 1750s by the Scottish physician Joseph Black. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. Black also found that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, English chemist Joseph Priestley published a paper entitled Impregnating Water with Fixed Air in which he described a process of dripping sulfuric acid (or oil of vitriol as Priestley knew it) on chalk in order to produce carbon dioxide, and forcing the gas to dissolve by agitating a bowl of water in contact with the gas.
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphry Davy and Michael Faraday. The earliest description of solid carbon dioxide was given by Charles Thilorier, who in 1834 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO2.
Carbon dioxide is produced mainly from six processes:
- From combustion of fossil fuels and wood;
- As a by-product of hydrogen production plants, where methane is converted to CO2;
- As a by-product of fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages;
- From thermal decomposition of limestone, CaCO3, in the manufacture of lime, CaO;
- As a by-product of sodium phosphate manufacture;
- Directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or dolomite.
Uses: Carbon dioxide bubbles in a soft drink.Carbon dioxide is used by the food industry, the oil industry, and the chemical industry. It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 bar (870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules are also sold as supplies of compressed gas for airguns, paintball markers, for inflating bicycle tires, and for making seltzer. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests, such as the Common Clothes Moth.
Some widespread uses: drinks, foods, pneumatic systems, fire extinguishers, welding, caffeine removal, pharmaceutical applications, agricultural and biological applications, lasers, polymers and plastics, oil recovery, refrigerants, coal bed methane recovery, wine making, pH control.
Carbon dioxide (CO2) forms approximately 0.04% of the nominal 5,000,000 gigatonnes of gas and aerosols that comprise the Earth's atmosphere. It is essential to photosynthesis in plants and other photoautotrophs, and is also a prominent greenhouse gas.
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. It is one of the most important cycles of the earth and allows for the most abundant element to be recycled and reused throughout the biosphere and all of its organisms.
Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars, fats and amino acids with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all plants, animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to the lungs where it is exhaled. In plants using photosynthesis, carbon dioxide is absorbed from the atmosphere.
Role in photosynthesis: Overview of photosynthesis and respiration. Carbon dioxide (at right), together with water, form oxygen and organic compounds (at left) by photosynthesis, which can be respired to water and (CO2).Plants remove carbon dioxide from the atmosphere by photosynthesis, also called carbon assimilation, which uses light energy to produce organic compounds (cellulose, lipids, and various proteins) by combining carbon dioxide and water. Free oxygen is released as gas from the decomposition of water molecules, while the hydrogen is split into its protons and electrons and used to generate chemical energy via photophosphorylation. This energy is required for the fixation of carbon dioxide in the Calvin cycle to make 3-phosphoglycerate that is used in metabolism, to construct sugars that can be used as an energy source within the plant through respiration and as the raw material for the construction of more complex organic molecules, such as polysaccharides, nucleic acids and proteins during growth.
Plants can grow up to 50 percent faster in concentrations of 1,000 ppm CO2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients. Some people (for example David Bellamy) believe that as the concentration of CO2 rises in the atmosphere that it will lead to faster plant growth and therefore increase food production. Such views are controversial. Studies have shown that increased CO2 leads to fewer stomata developing on plants which leads to reduced water usage. Studies using FACE have shown that increases in CO2 lead to decreased concentration of micronutrients in crop plants. This may have knock-on effects on other parts of ecosystems as herbivores will need to eat more food to gain the same amount of protein.
Plants also emit CO2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are only net absorbers during the day. Though a growing forest will absorb many tons of CO2 each year, the World Bank writes that a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g. fallen branches) as is used in biosynthesis in growing plants. However six experts in biochemistry, biogeology, forestry and related areas writing in the science journal Nature that "Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral." Mature forests are valuable carbon sinks, helping maintain balance in the Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean and thereby promotes the absorption of CO2 from the atmosphere.
Toxicity: Hypercapnia or hypercapnea (from the Greek hyper = "above" and kapnos = "smoke"), also known as hypercarbia, is a condition where there is too much carbon dioxide (CO2) in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. Hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, as in sudden infant death syndrome.
An arterial blood gas (ABG) is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or other sites are used. The blood can also be drawn from an arterial catheter. The test is used to determine the pH of the blood, the partial pressure of carbon dioxide and oxygen, and the bicarbonate level. Many blood gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin. ABG testing is mainly used in pulmonology, to determine gas exchange levels in the blood related to lung function, but has a variety of applications in other areas of medicine. Combinations of disorders can be complex and difficult to interpret, so calculators, nomograms, and rules of thumb are commonly used.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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