Increasing the surface area of a reactant affects the rate of a chemical reaction by increasing the number of particles of the reactant that are exposed and available to collide with other reactant particles. This leads to a higher frequency of collisions between reactant particles, which in turn increases the likelihood of successful collisions that result in the formation of products.In other words, a larger surface area allows for more opportunities for reactant particles to interact with each other, thus increasing the reaction rate. This is why, for example, grinding a solid reactant into a fine powder or using a highly dispersed catalyst can significantly speed up a chemical reaction.