Carbon dioxide is a naturally occurring chemical compound. It is inorganic in nature. The chemical formula is CO2. This compound exists in the Earth's atmosphere as a trace gas. In this state, it has a concentration of 0.039% by volume. One molecule of carbon dioxide contains 2 oxygen atoms which are bonded covalently with a single atom of carbon. At standard pressure and temperature, carbon dioxide is a gas. The concentration of this gas in the atmosphere fluctuates with season change. During summer and spring, the level of carbon dioxide drops as it is consumed by the plants in higher amounts. CO2 concentration increases during winter and autumn when the plants become dormant. CO2 is considered to be a greenhouse gas as it can badly impact the Earth's environment. It can transmit visible light and strongly absorbs infrared. Carbon dioxide has several commercial purposes.
In 1630, carbon dioxide was discovered by Flemish scientist Jan Baptista van Helmont (1580–1644). He was the first to identify a gas emitted by burning wood. He named it "sylvestre" meaning "wood gas". Van Helmont also recognized that wood gas was a combination of gases, not a single gas. In 1756, Scottish chemist Joseph Black proved the existence of carbon dioxide in the atmosphere. He also proved that carbon dioxide could form other compounds. He identified CO2 in the breath exhaled by humans. In 1823, Michael Faraday and Humphry Davy liquefied carbon dioxide for the first time.
During photosynthesis, carbon dioxide along with light and water is absorbed by plants, algae, and cyanobacteria to produce carbohydrate energy. Oxygen is released as a waste product. Carbon dioxide is a by-product of combustion and respiration. It is also emitted from hot springs, volcanoes and geysers. It is chemically extracted from carbonate rocks by dissolution. Carbon dioxide is also generated during thermal power generation. Extraction and refinement of hydrocarbons also releases carbon dioxide.
Carbon dioxide does not have any color. At low concentrations, carbon dioxide is odorless. At higher concentrations, carbon dioxide has a sharp, acidic odor. This can result in irritation and asphyxiation. If carbon dioxide is inhaled at higher concentrations (more than normal atmospheric levels), one can experience a stinging sensation in the throat and nose. This happens as the gas dissolves in the saliva and the mucous membrane forming a weak solution of carbonic acid. Drinking carbonated beverages can also result in such sensations. Over 50,000 ppm of carbon dioxide is considered to be highly unhealthy. Carbon dioxide molecule has a linear shape. It has two double bonds. It is completely oxidized and does not contain any electrical dipole.
At normal atmospheric pressure and −78.51 °C, carbon dioxide changes from a solid state to a gaseous phase. Solid carbon dioxide is commonly known as "dry ice." In the year 1825, dry ice was discovered by the French chemist Charles Thilorier. It is used as a cooling agent in grocery units, laboratories and shipping industry. Solid carbon dioxide is used for blast cleaning.
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