The rates of chemical reactions are determined by molecular collisions.
Section 1: Reaction rates and Rate Laws
The rate of a reaction refers to the rate at which reactants are converted to products and is given in terms of change in concentration versus time. There are several factors that affect the rates of reactions and rates must be experimentally determined. Reaction rates are often summarized mathematically in rate law expressions.
Section 2: Reactions occurring in a step-wise manner
By observing what the reactants and products are, or how they are converted from one to the other, we can classify most chemical reactions into 4 different categories. By classifying reactions we gain some predictive power as to what products could be formed.
Section 3: All the elementary steps add up to: The reaction mechanism
Understanding that most reactions proceed via elementary steps. The combination of all of the steps is called the reaction mechanism and the steps should add up to the overall reaction. As with life, the overall reaction is still rate-limited by the slowest elementary step in the mechanism and this step determines the overall rate law.