reaktioketjua

Reaktioketju is a concept in chemistry that describes a sequence of chemical reactions in which intermediates produced in one step are consumed in subsequent steps to form final products. The term is used across fields such as organic synthesis, combustion, atmospheric chemistry, and polymerization. In Finnish texts, the concept is called reaktioketju, with the partitive form reaktioketjua.

Two common forms of reaktioketjuja are consecutive (series) reactions and chain reactions. In consecutive reactions, species pass through a defined sequence A -> B -> C, with the overall product arising from the cumulative steps. In chain reactions, reactive intermediates propagate the sequence by regenerating reactive species that continue to react with other molecules, allowing the chain to continue with limited external input. Chain reactions may also involve branching, where a single intermediate can produce multiple new reactive species, influencing the overall rate and product distribution. Termination steps remove reactive intermediates and halt the chain.

Radical chain reactions illustrate the mechanism nicely. Initiation forms radicals that drive propagation steps, such as abstraction or addition reactions, which regenerate reactive species and sustain the sequence. Termination occurs when two radicals combine or disproportionate, ending the chain. Similar chain processes occur in polymerization, where active centers add monomer units in propagation steps to grow polymer chains until termination.

Understanding reaktioketjuja requires kinetic modelling to describe initiation, propagation, branching, and termination steps. Practical considerations include control of chain length and selectivity, as well as safety concerns, since chain reactions can be highly exothermic and sensitive to impurities and temperature changes.

See also: reaction mechanism, chemical kinetics, radical reactions, polymerization, chain reaction, branching.