Differentiate between Complex reaction and elementary reaction?

Complex reactions and elementary reactions are two different types of chemical reactions that occur in chemical kinetics. Here's how they differ:

Elementary Reaction:
An elementary reaction, also known as a simple reaction or a single-step reaction, is a chemical reaction that occurs in a single step or a single molecular collision.
It is represented by a balanced chemical equation that directly shows the reactants being converted into products without any intermediates.
Elementary reactions are typically characterized by their simple reaction mechanisms and well-defined reaction orders with respect to each reactant.
The rate law for an elementary reaction can be directly determined from the coefficients of the reactants in the balanced equation.
Elementary reactions are often used as building blocks for more complex reaction mechanisms.
Example of an elementary reaction:
A + B → C (with a rate law of rate = k[A][B])

Complex Reaction:
A complex reaction, also known as a composite reaction or a multi-step reaction, involves multiple intermediate steps before the final products are formed.
Complex reactions are represented by a series of elementary reactions (multiple steps) that describe the overall reaction mechanism.
These reactions often have intermediates, which are unstable species that form during the reaction and are consumed in subsequent steps.
The rate law for a complex reaction is determined by the rate-determining step (the slowest step) in the mechanism.
Complex reactions are common in organic chemistry and biochemistry, where many reactions involve multiple steps.
Example of a complex reaction:
2NO2 → N2O4 (with a mechanism involving multiple elementary steps, such as the formation of NO3 radicals as intermediates)

In summary, the key difference between complex and elementary reactions lies in the number of steps involved in the reaction mechanism. Elementary reactions occur in a single step, while complex reactions involve multiple intermediate steps. Complex reactions are often described by a series of elementary reactions that collectively represent the overall reaction.