reaction mechanism
The overall balanced equation for a chemical reaction does not always tell us how a reaction actually proceeds. In many cases, the overall reaction takes place in a series of small steps. An elementary step or elementary reaction is one step in a series of simple reactions that show the progress of a reaction at the molecular level. In terms of collision theory, each elementary step corresponds to a single collision. A reaction mechanism is the sequence of elementary steps that together comprise an entire chemical reaction. As an analogy, consider the route that you might take while driving to the grocery store. That route may consist of several turns, similar to the elementary steps. The overall reaction specifies only the beginning point your house and the final destination the store , with no information about the specifics in between.