Which statement best describes how reactant concentration affects collision theory?

• A. The more moles of reactant present, the increased likelihood of a collision.
• B. Collisions occur only when temperature is high.
• C. The rate is independent of concentrations of reactants.
• D. The presence of a catalyst changes collision frequency.

Answer: (A)

Increasing reactant concentration raises how often reactant molecules run into each other. In collision theory, the reaction rate is tied to the frequency of collisions that have enough energy to overcome the activation barrier and the right orientation to react. So, when you have more particles in the same space, collisions happen more often, and there are more opportunities for those effective collisions, raising the rate while temperature stays the same.

Colissions occur across temperatures, but not all collisions are energetic enough to react; raising temperature increases the fraction that are effective, which is why the statement about collisions only happening at high temperature isn’t accurate. The rate does depend on concentrations of reactants, so saying it’s independent is incorrect. A catalyst changes the pathway and lowers the activation energy, increasing the likelihood that a collision leads to product, but it doesn’t inherently increase how often collisions happen due to concentration, so it doesn’t describe the concentration effect.