The mechanism of a reaction is a detailed description of the way a reaction occurs. It is a sequence of elementary steps which lead from reactants to products. There are variables which affect reaction rates.
Many reactions take place in a fraction of a second others take years.
The characteristics of the reactants and the products. The concentration of the reactants - in some reactions the rate is unaffected by the concentration of a particular reactant as long as it is there in some amount. The presence of a catalyst, a substance that increases the rate of reaction without being consumed in the overall reaction, affects the rate. The temperature at which the reaction occurs. Usually reactions increase in rate when the temperature increases.