ketjureaktion

Ketjureaktion is the Finnish term for a chain reaction, a sequence of reactions in which the product of one step triggers subsequent steps, creating a self-sustaining cascade. The base term ketjureaktio means "chain reaction," and ketjureaktion is the genitive form used to denote "of the chain reaction."

In chemistry, chain reactions are typically described by initiation, propagation, and termination. Initiation creates reactive intermediates, such as free radicals, that enter propagation steps to produce more reactive species and new products. Termination occurs when reactive intermediates are removed from the system, ending the sequence. A classic example is the free-radical chlorination of methane, where chlorine atoms generated in initiation propagate multiple times before being quenched.

In nuclear physics, a chain reaction occurs when a fission event releases neutrons that cause further fissions in nearby nuclei. If the system is capable of producing, on average, at least one new fission per event, the reaction can become self-sustaining (critical). Control in reactors is achieved with moderators, reflectors, and neutron-absorbing materials to keep the reaction subcritical or carefully at a desired critical state.

Chain reactions also arise in polymer chemistry (chain-growth polymerization) and in autocatalytic biochemical networks. They can release large amounts of energy; uncontrolled reactions pose safety risks, including explosions or thermal runaway. Proper design, monitoring, and safety protocols are essential in industrial and research settings.