chain reaction

Dictionary: chain reaction

A series of events in which each induces or influences the next.
Physics. A multistage nuclear reaction, especially a self-sustaining series of fissions in which the release of neutrons from the splitting of one atom leads to the splitting of others.
Chemistry. A series of reactions in which one product of a reacting set is a reactant in the following set.

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Britannica Concise Encyclopedia: chain reaction

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Process yielding products that initiate further processes of the same kind. Nuclear chain reactions are a series of nuclear fissions initiated by neutrons produced in a preceding fission. A critical mass, large enough to allow more than one fission-produced neutron to be captured, is necessary for the chain reaction to be self-sustaining. Uncontrolled chain reactions, as in an atomic bomb, occur when large numbers of neutrons are present and the reactions multiply very quickly. Nuclear reactors control their reactions through the careful distribution of the fissionable material and insertion of neutron-absorbing materials.

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Sci-Tech Encyclopedia: Chain reaction

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physical chemistry
nuclear physics

(physical chemistry)

A chemical reaction in which many molecules undergo chemical reaction after one molecule becomes activated. In ordinary chemical reactions, every molecule that reacts must first become activated by collision with other rapidly moving molecules. The number of these violent collisions per second is so small that the reaction is slow. After a chain reaction is started, it is not necessary to wait for more collisions with activated molecules to accelerate the reaction because the reaction now proceeds spontaneously.

A typical chain reaction is the photochemical reaction between hydrogen and chlorine as described by the following reactions.
$\rm Cl_2 + light \to Cl + Cl$

$\rm Cl + H_2 \to HCl + H$

$\rm H + Cl_2 \to HCl + Cl$

$\rm Cl + H_2 \to HCl + H$

The light absorbed by a chlorine molecule dissociates the molecule into chlorine atoms; these in turn react rapidly with hydrogen molecules to give hydrogen chloride and hydrogen atoms. The hydrogen atoms react with chlorine molecules to give hydrogen chloride and chlorine atoms. The chlorine atoms react further with hydrogen and continue the chain until some other reaction uses up the free atoms of chlorine or hydrogen. The chain-stopping reaction may be the reaction between two chlorine atoms to give chlorine molecules, or between two hydrogen atoms to give hydrogen molecules. Again the atoms may collide with the walls of the containing vessel, or they may react with some impurity which is present in the vessel only as a trace.

Certain oxidations in the gas phase are known to be chain reactions. The carbon knock which occurs at times in internal combustion engines is caused by a too-rapid combustion rate caused by chain reactions. This chain reaction is reduced by adding tetraethyllead, which acts as an inhibitor.

The polymerization of styrene to give polystyrene and the polymerization of other organic materials to give industrial plastics involve chain reactions. The spoilage of foods, the precipitation of insoluble gums in gasoline, and the deterioration of certain plastics in sunlight involve chain reactions, which can be minimized with inhibitors. See also Chemical dynamics; Photochemistry.

Chain reaction (nuclear physics)

A succession of generation after generation of acts of division (called fission) of certain heavy nuclei. The fission process releases about 200 MeV (3.2 × 10⁻⁴ erg = 3.2 × 10⁻¹¹ joule) in the form of energetic particles including two or three neutrons. Some of the neutrons from one generation are captured by fissile species (²³³U, ²³⁵U, ²³⁹Pu) to cause the fissions of the next generations. The process is employed in nuclear reactors and nuclear explosive devices.

Idioms: chain reaction

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A series of events in which each influences or gives rise to the next event, as in If one person collects substantial damages by suing a company, you can expect a chain reaction of such lawsuits. The term originated in the physical sciences, first (1920s) chemistry and later (1940) physics; in the latter it denotes a process of nuclear fission. By the 1940s it had been transferred to more general use.

US Military Dictionary: chain reaction

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The self-sustaining fission reaction spread by neutrons that occurs in nuclear reactors and bombs.

See the Introduction, Abbreviations and Pronunciation for further details.

Columbia Encyclopedia: chain reaction

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chain reaction, self-sustaining reaction that, once started, continues without further outside influence. Proper conditions for a chain reaction depend not only on various external factors, such as temperature, but also on the quantity and shape of the substance undergoing the reaction. A chain reaction can be of various types, but nuclear chain reactions are the best known. A line of dominoes falling after the first one has been pushed is an example of a mechanical chain reaction; a pile of wood burning after it has been kindled is an example of a chemical chain reaction. In the latter case each piece of wood, as it burns, must release enough heat to raise nearby pieces to the kindling point. The wood, therefore, must be piled close enough together so that not too much heat is lost to the surrounding air. The conditions for a nuclear chain reaction can be understood by analogy. In the case of the fission of a nucleus, the reaction is begun by the absorption of a slow neutron. Each fission produces two or three fast neutrons. In order to sustain a chain reaction, a sample must be large enough to slow the neutrons so that one can be captured by another nucleus and produce a second fission. The sample must also be compact to prevent neutrons from escaping. The minimum quantity of a fissionable material necessary to sustain a nuclear chain reaction is called the critical mass. In a nuclear fission bomb, a chain reaction is started by forcing together two or more samples of fissionable material, each of less than critical mass, to form one sample of supercritical mass. The number of subsequent fissions produced by a single fission is always greater than one. The total number of fissions increases rapidly (exponentially) with time. In a fission reactor, the number of subsequent fissions for each fission must be exactly one. If the rate is less, the chain reaction will stop; if greater, it will soon grow out of control. In one type of fission reactor, a combination of fuel rods and control rods is moved in or out of a solid block of moderating material to control the reaction rate. In another type of reactor, the temperature of a liquid moderator controls the reaction. See also nuclear energy; nuclear reactor.

Science Dictionary: chain reaction

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In chemistry and physics, a self-sustaining series of reactions. In a chain reaction in a uranium-based nuclear reactor, for example, a single neutron causes the nucleus of a uranium atom to undergo fission. In the process, two or three more neutrons are released. These neutrons start more fissions, which produce more neutrons, and so on.

Figuratively speaking, any group of events linked so that one is the cause of the next can be called a “chain reaction.”

Wikipedia: Chain reaction

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This article is about chain reactions in chemistry and physics. For other uses, see Chain reaction (disambiguation).

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. Examples of chain reactions include:

The neutron-fission chain reaction: a neutron plus a fissionable atom causes a fission resulting in a larger number of neutrons than was consumed in the initial reaction. This reaction could continue if the number of neutron produced in a single reaction is capable of producing another fission. If not the reaction will stop. If the number of fissions produced is more than one then the reaction is said to be supercritical and the number of fissions would increase exponentially. This is the principle for an atomic bomb.
For example in a chemical reaction every step of H₂ + Cl₂ chain reaction consumes one molecule of H₂ or Cl₂, one free radical H· or Cl· producing one HCl molecule and another free radical.
Electron avalanche process: Collisions of free electrons in a strong electric field releasing "new" electrons to undergo the same process in successive cycles.
A cascading failure, a failure in a system of interconnected parts, for example a power transmission grid, where the service provided depends on the operation of a preceding part, and the failure of a preceding part can trigger the failure of successive parts.
Polymerase chain reaction, a technique used in molecular biology to amplify (make many copies of) a piece of DNA by in vitro enzymatic replication using a DNA polymerase.

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		Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more
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