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How does a chain reaction continue after an initiating step?

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dissociation of E–N — reaction mechanism Possible energy diagram for the dissociation of a covalent molecule, E–N, into its ions E⁺ and N⁻ (see text).

After the initiation step, a chemical chain reaction continues through a process known as propagation.12

During this stage, the reactive intermediate formed during initiation—such as an atom, ion, or free radical—reacts with the original reactants. This interaction produces stable products and generates a new reactive intermediate. Because this new intermediate is capable of reacting just as the previous one did, a repetitive cycle is established, allowing the reaction to sustain itself.12

In some cases, this cycle involves the continuous regeneration of the intermediate, meaning a single reactive species can lead to the production of many product molecules. If the number of chain carriers increases during each propagation step, the process is called a branching chain reaction, which can cause the reaction to accelerate rapidly. This cycle continues until a termination step occurs, where the chain carriers are consumed or recombined, often due to the depletion of reactants or the introduction of inhibitors.312