Which factor does NOT affect the rate of a reaction?

The rate of a chemical reaction is influenced by several factors, including the concentration of reactants, temperature, and the presence of a catalyst. These factors affect how often molecules collide and the energy of these collisions.

The concentration of reactants plays a crucial role because a higher concentration increases the number of particles in a given volume, leading to more frequent collisions and a faster reaction rate. Temperature affects the kinetic energy of the particles; as temperature rises, particles move faster, leading to more collisions and increased energy during those collisions, which can also speed up the reaction. A catalyst provides an alternative reaction pathway with a lower activation energy, effectively increasing the rate of reaction without being consumed in the process.

In contrast, the color of reactants does not influence the rate of a reaction. While it can provide visual information about the reactants or the progress of a reaction, it does not affect the kinetic or thermodynamic properties involved in reaction rates. Therefore, this factor does not have a direct impact on how quickly a reaction occurs.