A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. It is a self-amplifying chain of events.
The neutron-fissionchain 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 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.
