According to the collision theory, the rate of a chemical reaction is affected by four factors: temperature, surface area, concentration, and catalysts.

• Temperature: An increase in temperature generally increases the rate of a reaction. Particles at a high temperature have more energy of motion than do particles at a low temperature. Particles at a high temperature move faster, and collide more frequently and with greater energy, thus increasing the reaction rate. More particles of reactants are able to gain the activation energy needed to form products. At room temperature, the rates of many chemical reactions roughly double or triple with a rise in temperature of 10°C.

• Surface Area: Surface area refers to how much of a material is exposed. An increase in surface area increases the collisions between reacting particles.

• Concentration: The concentration of a substance is a measure of the amount of that substance in a given unit of volume. A high concentration of reactants means there are a great many particles per unit volume. Since there are more particles of reactants available for collisions, more products are formed in a certain amount of time.

• Catalysts: A catalyst is a substance that increases the rate of a reaction but is not itself changed by the reaction. Reactions are based on a series of steps. A catalyst changes one or more of the steps. A catalyst produces a different, lower energy path for the reaction by lowering the activation energy. This decrease allows more reactant particles to form products. Catalysts are usually involved in one or more of the early steps in a reaction and then reformed in a later step. This explains why a catalyst can be recovered at the end of the reaction. Catalysts are rare and are specific to certain reactions.