1. Chemical Natures of Reactants
Depending on the natures of the substances that are reacted, reaction rates may vary. For example, acid/base reactions usually occur quickly, where as oxidation of iron occurs over a long period of time
2. Surface Area
For heterogeneous reactions— reactions where the reactants are in different states— reaction can only occur at the surface between the two states. Therefore, the larger the surface area, the faster the reaction rate.
3. Concentration
According to the collision theory, reactions can only occur when molecules collide. If the concentrations of the reactants are higher, there will be more collisions, and thus the reaction rate will increase. It is one of the most common methods of changing reaction rates.
4. Temperature
At a greater temperature, molecules will have more kinetic energy. This not only means that collisions will be more frequent, but also that more molecules will have sufficient energy to reactant when they collide
5. Catalyst
A catalyst changes the reaction mechanism such that the activation energy (energy required for the molecules to react) is lower. This means that more molecules will have sufficient energy to react when they collide.
