Chemistry Regents Practice Test

Which factor primarily determines the rate of a chemical reaction?

1. Color of the reactants

2. Concentration of the reactants

3. Volume of the reaction mixture

4. Mass of the reactants

The correct answer is: Concentration of the reactants

The concentration of the reactants is a key factor that primarily determines the rate of a chemical reaction. When the concentration of reactants is increased, there are more reactant molecules available to collide with each other. Chemical reactions occur when reactant particles collide with sufficient energy and proper orientation. Thus, higher concentrations lead to more frequent collisions, which increases the likelihood of successful reactions occurring over a given time. Conversely, factors such as the color of the reactants or their mass do not fundamentally affect the actual rate at which the reaction takes place. The volume of the reaction mixture can influence the concentration (and therefore indirectly affect the reaction rate), but it is not itself a direct determinant of the reaction rate. The primary influence is indeed the concentration, as it directly correlates with the frequency of collisions among reactive particles.