A chain reaction is a sequence of reactions where a reactive product or biproduct causes more additional reactions.

Examples:

• 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.
• Chemical reactions, where a product of a reaction is itself a reactive particle which can cause more similar reactions. For example, 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.

See also

• Nuclear chain reaction
• Polymerase chain reaction
• Chain Reaction (film)