reactants
Concentration Effects Two substances cannot possibly react with each other unless their constituent particles molecules, atoms, or ions come into contact. If there is no contact, the reaction rate will be zero. Conversely, the more reactant particles that collide per unit time, the more often a reaction between them can occur. Consequently, the reaction rate usually increases as the concentration of the reactants increases. One example of this effect is the reaction of sucrose table sugar with sulfuric acid, which is shown in Figure 14.1 "The Effect of Concentration on Reaction Rates".