reactieketen

Reactieketen refers to a sequence of chemical reactions where reactive intermediates are formed and consumed in the same overall process, forming a chain. They are common in free-radical chemistry, polymerization, combustion, and atmospheric chemistry. The key idea is that a reactive intermediate generated in one step continues to react in subsequent steps, propagating the chain.

The mechanism is typically described as three parts: initiation, propagation, and termination. Initiation produces reactive intermediates (often radicals) by homolytic bond cleavage or redox processes. In propagation, these intermediates react with stable molecules to form new intermediates, perpetuating the chain. Termination occurs when reactive intermediates are consumed without regenerating others, ending the chain sequence. Some chains can branch if a single intermediate can produce multiple new radicals.

Examples include free-radical polymerization, where radicals add monomers to form growing chains; hydrogen-oxygen combustion chain reactions; and atmospheric radical cycles (HOx, ROx) that drive ozone formation and degradation. In polymerization, chain length and rate depend on the balance between initiation, propagation, and termination rates, as well as inhibitors and chain-transfer agents.

Practical significance: understanding reactieketen can help control reaction rates, selectivity, and safety. Inhibitors or chain-transfer agents are used to regulate chain growth; chain termination steps control final product properties. In research, kinetic modeling of chain reactions uses rate constants for initiation, propagation, and termination.