Editing Nuclear chain reaction (section)

===Reaction products===
When a fissile atom undergoes nuclear fission, it breaks into two or more fission fragments. Also, several free neutrons, [[gamma ray]]s, and [[neutrino]]s are emitted, and a large amount of energy is released. The sum of the rest masses of the fission fragments and ejected neutrons is less than the sum of the rest masses of the original atom and incident neutron (of course the fission fragments are not at rest). The mass difference is accounted for in the release of energy according to the equation [[Mass–energy equivalence|''E=Δmc<sup>2</sup>'']]:

:'''mass of released energy''' = <math>\frac{E}{c^2} = m_\text{original}-m_\text{final}</math>

Due to the extremely large value of the [[speed of light]], ''c'', a small decrease in mass is associated with a tremendous release of active energy (for example, the kinetic energy of the fission fragments). This energy (in the form of radiation and heat) carries the missing mass when it leaves the reaction system (total mass, like total energy, is always [[conservation of mass|conserved]]). While typical chemical reactions release energies on the order of a few [[electron volt|eVs]] (e.g. the binding energy of the electron to hydrogen is 13.6&nbsp;eV), nuclear fission reactions typically release energies on the order of hundreds of millions of eVs.

Two typical fission reactions are shown below with average values of energy released and number of neutrons ejected:

:<math chem>\begin{align}
\ce{^{235}U + neutron ->} &\ \text{fission fragments} + 2.4\text{ neutrons} + 192.9\text{ MeV} \\
\ce{^{239}Pu + neutron ->} &\ \text{fission fragments} + 2.9\text{ neutrons} + 198.5\text{ MeV}
\end{align}</math><ref name=Duderstadt>{{cite book |last=Duderstadt |first=James |author2=Hamilton, Louis  |title=Nuclear Reactor Analysis |year=1976 |publisher=John Wiley & Sons, Inc |isbn=978-0-471-22363-4 }}</ref>

Note that these equations are for fissions caused by slow-moving (thermal) neutrons. The average energy released and number of neutrons ejected is a function of the incident neutron speed.<ref name=Duderstadt /> Also, note that these equations exclude energy from [[Neutrino|neutrinos]] since these subatomic particles are extremely non-reactive and therefore rarely deposit their energy in the system.