Reactions proceed by a series of simple steps called elementary processes involving 1 or 2 particles at a time. A series of elementary processes is a reaction mechanism
The slowest step (elementary process) is the rate determining step for the overall reaction
Example
Making Pizza Make Dough → Put Toppings → Bake Pizza → Cut Pizza
Baking the pizza is the longest Step (rate determining step)
Reaction Intermediate: part of the reaction but not part of the overall equation. In this case its
