Changes

[[File:lighterstill.jpg]][[File:Fission_chain.jpg|right|frame]]

[[File:lighterstill.jpg]][[File:Fission_chain.jpg|right|frame]]

*[http://en.wikipedia.org/wiki/20th_century 1902]

*[https://en.wikipedia.org/wiki/20th_century 1902]

==Definitions==

==Definitions==

*1a : a [[series]] of [[events]] so related to each other that each one [[initiates]] the next  

*1a : a [[series]] of [[events]] so related to each other that each one [[initiates]] the next  

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]].

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 thermodynamic non-equilibrium can release [[energy]] or increase [http://en.wikipedia.org/wiki/Entropy 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 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.

Chain reactions are one way in which [[systems]] which are in thermodynamic non-equilibrium can release [[energy]] or increase [https://en.wikipedia.org/wiki/Entropy 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 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 macrosopic [[metaphor]] for chain reactions is thus a snowball causing larger snowfall until finally an [http://en.wikipedia.org/wiki/Avalanche avalanche] results ("snowball effect"). 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 [http://en.wikipedia.org/wiki/Neutron neutron] can result in a [http://en.wikipedia.org/wiki/Prompt_critical prompt critical] event, which may be finally be energetic enough for a nuclear reactor meltdown or (in a bomb) a nuclear [[explosion]]. However, this reaction cannot be reversed.[http://en.wikipedia.org/wiki/Chain_reaction]

A macrosopic [[metaphor]] for chain reactions is thus a snowball causing larger snowfall until finally an [https://en.wikipedia.org/wiki/Avalanche avalanche] results ("snowball effect"). 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 [https://en.wikipedia.org/wiki/Neutron neutron] can result in a [https://en.wikipedia.org/wiki/Prompt_critical prompt critical] event, which may be finally be energetic enough for a nuclear reactor meltdown or (in a bomb) a nuclear [[explosion]]. However, this reaction cannot be reversed.[https://en.wikipedia.org/wiki/Chain_reaction]

[[Category: Physics]]

[[Category: Physics]]