Chain reaction - Wikipedia. A chain reaction is a sequence of reactions where a reactive product or by- product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self- amplifying chain of events. Chain reactions are one way in which systems which are in thermodynamicnon- equilibrium can release energy or increase entropy in order to reach a state of higher entropy. For example, a system may not be able to reach a lower energy state by releasing energy into the environment, because it is hindered or prevented in some way from taking the path that will result in the energy release. If a reaction results in a small energy release making way for more energy releases in an expanding chain, then the system will typically collapse explosively until much or all of the stored energy has been released. A macroscopic metaphor for chain reactions is thus a snowball causing a larger snowball until finally an avalanche results (. This is a result of stored gravitational potential energy seeking a path of release over friction. Chemically, the equivalent to a snow avalanche is a spark causing a forest fire. In nuclear physics, a single stray neutron can result in a prompt critical event, which may be finally be energetic enough for a nuclear reactor meltdown or (in a bomb) a nuclear explosion. Chemical chain reactions. If two molecules react, not only molecules of the final reaction products are formed, but also some unstable molecules which can further react with the parent molecules with a far larger probability than the initial reactants. In the new reaction, further unstable molecules are formed besides the stable products, and so on. In 1. 91. 8, Walther Nernst proposed that the photochemical reaction of hydrogen and chlorine is a chain reaction in order to explain the large quantum yield, meaning that one photon of light is responsible for the formation of as many as 1. HCl. He suggested that the photon dissociates a Cl. Chain reaction, in chemistry and physics, process yielding products that initiate further processes of the same kind, a self-sustaining sequence. Examples from chemistry are burning a fuel gas, the development of rancidity in.Cl atoms which each initiate a long chain of reaction steps forming HCl. The result is in fact an exponential growth, thus giving rise to explosive increases in reaction rates, and indeed to chemical explosions themselves. This was the first proposal for the mechanism of chemical explosions. CHAIN REACTION II How Top Restaurants Rate on Reducing Use of Antibiotics in Their Meat Supply. A quantitative chain chemical reaction theory was created by Soviet physicist Nikolay Semyonov in 1. In effect the active particle serves as a catalyst for the overall reaction of the propagation cycle. Particular cases are: * chain branching (a propagation step which forms more new active particles than enter the step); * chain transfer (a propagation step in which the active particle is a growing polymer chain which reacts to form an inactive polymer whose growth is terminated and an active small particle (such as a radical), which may then react to form a new polymer chain). Termination (elementary step in which the active particle loses its activity; e. The propagation is a sequence of two steps whose net effect is to replace an H atom by another H atom plus two OH radicals. Chain Reaction, also known as The Strangeurs, was an American pop band from Yonkers, New York. They had two singles and were most notable for having lead singer Steven Tallarico (Steven Tyler, as he would later come to be. This leads to an explosion under certain conditions of temperature and pressure. Chain transfer corresponds to transfer of the activity from this growing chain, whose growth is terminated, to another molecule which may be a second growing polymer chain. For polymerization, the kinetic chain length defined above may differ from the degree of polymerization of the product macromolecule. Polymerase chain reaction, a technique used in molecular biology to amplify (make many copies of) a piece of DNA by in vitroenzymaticreplication using a DNA polymerase. Nuclear chain reactions. This would in theory produce a chain reaction at the level of the nucleus. He did not envision fission as one of these neutron- producing reactions, since this reaction was not known at the time. Experiments he proposed using beryllium and indium failed. Later, after fission was discovered in 1. Szil. In 1. 93. 9, with Enrico Fermi, Szil. In this reaction, a neutron plus a fissionable atom causes a fission resulting in a larger number of neutrons than the single one that was consumed in the initial reaction. Thus was born the practical nuclear chain reaction by the mechanism of neutron- induced nuclear fission. Specifically, if one or more of the produced neutrons themselves interact with other fissionable nuclei, and these also undergo fission, then there is a possibility that the macroscopic overall fission reaction will not stop, but continue throughout the reaction material. This is then a self- propagating and thus self- sustaining chain reaction. This is the principle for nuclear reactors and atomic bombs. Demonstration of a self- sustaining nuclear chain reaction was accomplished by Enrico Fermi and others, in the successful operation of Chicago Pile- 1, the first artificial nuclear reactor, in late 1. Electron avalanche in gases. Random thermal collisions of gas atoms may result in a few free electrons and positively charged gas ions, in a process called impact ionization. Acceleration of these free electrons in a strong electric field causes them to gain energy, and when they impact other atoms, the energy causes release of new free electrons and ions (ionization), which fuels the same process. If this process happens faster than it is naturally quenched by ions recombining, the new ions multiply in successive cycles until the gas breaks down into a plasma and current flows freely in a discharge. Electron avalanches are essential to the dielectric breakdown process within gases. The process can culminate in corona discharges, streamers, leaders, or in a spark or continuous electric arc that completely bridges the gap. The process may extends to huge sparks . Once begun, avalanches are often intensified by the creation of photoelectrons as a result of ultraviolet radiation emitted by the excited medium's atoms in the aft- tip region. The extremely high temperature of the resulting plasma cracks the surrounding gas molecules and the free ions recombine to create new chemical compounds. This is the mechanism of a Geiger counter and also the visualization possible with a spark chamber and other wire chambers. Avalanche breakdown in semiconductors. Semiconductors rely on free electrons knocked out of the crystal by thermal vibration for conduction. Thus, unlike metals, semiconductors become better conductors the higher the temperature. This sets up conditions for the same type of positive feedback. This can continue to the point of complete breakdown of normal resistance at a semiconductor junction, and failure of the device (this may be temporary or permanent depending on whether there is physical damage to the crystal). Certain devices, such as avalanche diodes, deliberately make use of the effect. In economics. And economic collapse often has the character of a cumulative process. Let it go beyond a certain point, and it will tend for a time to gain strength from its own development as its effects spread and return to intensify the process of collapse. Freeman 2. 00. 6), p. ISBN 0- 7. 16. 7- 8. Laidler K. J., Chemical Kinetics (3rd ed., Harper & Row 1. ISBN 0- 0. 6- 0. 43. Arc Suppression Technologies. Retrieved March 1. The Banking Crisis in USA: External links. Chain Reaction (1. Rotten Tomatoes. Just as the university research team is about to prove that their new technique will permit water to be used as a fuel, their laboratory is sabotaged and the lab manager is killed. Eddie Kasalivich (Keanu Reeves) stumbles onto the scene and manages not only to witness the sabotage, but to escape from it. When he tries to talk about it to authorities, he discovers that they think he and the other project survivors committed the crime. In reality, a group of energy companies have conspired with interested parties in the government to completely erase all notion of the existence of a way to use water as fuel. The project sponsor (Morgan Freeman) wants Eddie to turn himself in, but before he can do that, he must find enough evidence to clear himself and his friends. But in order to succeed, Eddie must avoid assassination attempts by the real perpetrators.
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