Which of the following conditions increases the frequency of collisions without changing the energy or concentration of reactants?

A: increasing the surface area of the substance

B: adding more reactant molecules

C: increasing the temperature

D: increasing the pressure

You can promote collisions between molecules when you increase their kinetic energy by either increasing the temperature or pressure conditions of the systems. However, it is indicated that you must not change the energy. So, we eliminate choices C and D. Choice B is contradictory to the limitation that you do not increase the concentration of the reactants. Technically, all of the choices promote frequent collisions. But due to the limitations set, the accepted answer is letter A. When you increase the surface area by using powdered reactants instead of cubes, you increase the areas for susceptibility of collisions.