officially recognized that in 1774, the English chemist Joseph Priestley had discovered oxygen (O2).As a result of experiments conducted in a closed vessel with mercuric oxide, under the action of sunlight directed by a lens, its expansion has occurred: 2HgO → O2 ↑ + 2Hg.It has a density gaseous under normal conditions 0.00142897 g / cm³, a molar volume of 14.0 cm³ / mole, a melting point minus 218.2 ° C and a boiling point of minus 182.81 ° C.The molar mass equals 15.9994 g / mol.The main characteristic of oxygen - is its ability to oxidize various substances.As an active non-metal, O2 reacts with all metals forming basic and amphoteric oxides, as well as all non-metals (other than halogen) to afford the acid or nesoleobrazuyuschie oxides.
Oxygen is part of more than a thousand agents, as is the most common chemical element on Earth.He is a member of various chemical compounds (there are more than one and a half thousand).The solid earth's crust O2 content equal to 47.4%.The marine and fresh waters of its share in a bound state falls 88.8% by weight.In an atmosphere of oxygen in a free state, it is equal to the volume fraction of about 21%, and the bulk - 23.1%.It is an important component of organic substances that are present in every living cell.By volume it occupies are 25% and 65% by weight.Circulation of oxygen in nature due to its chemical activity.
cycle is a series of changes of substance, as a result of which it returns to the starting point, and repeated all the way.Oxygen is the biogeochemical cycle of movement.Through it passes through O2 biotic sum of all ecosystems (the biosphere or the area of life on Earth) and abiotic (lithosphere, hydrosphere and atmosphere) environment.Circulation of oxygen describes his movement in the hydrosphere (water mass, located below ground and above its surface), atmosphere (air), the biosphere (global sum of all ecosystems) and the lithosphere (the crust).Violations of this cycle in the hydrosphere can lead to the development of hypoxic (low O2) zones in large lakes and the ocean.The main driving factor is photosynthesis.
ecological system (ecosystem) have a lot of biogeochemical cycles, working in their composition.For example, the water cycle, the cycle of oxygen, nitrogen cycle, carbon, etc.All chemical elements are the path that is part of the biogeochemical cycles.They are an integral part of living organisms, but also move through the abiotic environment ecosystems.This is the water (hydrosphere), the Earth's crust (the lithosphere) and the air (atmosphere).Living organisms fill the shell of the Earth called biosphere.All nutrients such as carbon, nitrogen, oxygen, phosphorus and sulfur, they are used and are part of a closed system, so they are recycled and not lost and replenished continuously, such as in an open system.
largest reservoir O2 (99,5%) is the crust and mantle of the Earth, where it is contained in silicate and oxide minerals.Circulation oxygen ingress provided only a small part in the form of free O2 in the biosphere (0.01%) and the atmosphere (0.36%).The main source of atmospheric O2 is free photosynthesis.Its products are organic matter and free oxygen is formed from carbon dioxide and water: 6CO2 + 6H2O + energy → C6H12O6 + 6O2.
For circulation of oxygen in the biosphere respond terrestrial plants, phytoplankton and oceans.Tiny marine cyanobacteria (blue-green algae) Prochlorococcus, the size of 0.6 microns, were discovered in 1986.They accounted for more than half of the products of photosynthesis in the open ocean.An additional source of free atmospheric oxygen is the phenomenon of photolysis (chemical reaction caused by the action of photons).As a result of atmospheric water and nitrous oxide are dissociated into its component atoms, hydrogen (H) and nitrogen (N) removed the space and O2 remains in the atmosphere: 2H2O + energy → 4H + O2 and 2N2O + energy → 4N + O2.Consumed oxygen free atmosphere of living organisms in the process of respiration and decay.Lithosphere using free O2 in the result of chemical weathering and surface reactions.For example, he spent on the formation of iron oxide (rust): 4FeO + O2 → 2Fe2O3 or other metal oxides and non-metals.
oxygen cycle also includes a loop between the biosphere and lithosphere.Marine organisms in the biosphere are sources of calcium carbonate (CaCO3), which is rich in O2.When an organism dies, its shell brought to the shallow waters of the seabed, where for a long time to form limestone (sedimentary rock of the earth's crust).Weathering processes initiated by the biosphere, it can also extract free oxygen from the lithosphere.Plants and animals extract nutrients from the sediment and release oxygen.
