What is a reaction mechanism?

A reaction mechanism describes the sequence of individual steps in a chemical reaction. In a chemical reaction, each step (known as an elementary reaction) involves one, two, or occasionally three atoms, molecules, or ions. The collective sequence of these elementary reactions constitute the reaction mechanism. It's essential that the sum of all elementary reactions within the mechanism yields the balanced chemical equation for the overall reaction. There is typically one step that proceeds much more slowly than the others, which is the rate-determining step.