Which statement best explains why increasing concentration increases the rate of reaction?

• A. More particles per unit volume
• B. Temperature rises
• C. Collisions become less frequent
• D. The activation energy increases

Answer: (A)

Increasing concentration raises the rate of a reaction because more particles are present in the same volume, so collisions between particles happen more often. Collision theory says reactions occur when particles collide with enough energy and proper orientation, so a higher collision frequency means more successful collisions per second and a faster rate. The statement about having more particles per unit volume best captures this effect of concentration.

If temperature were increased, the rate would also rise due to greater kinetic energy, but that changes energy of collisions rather than how often they occur. Saying collisions become less frequent contradicts the idea that more particles lead to more collisions. Increasing activation energy would make it harder for collisions to be successful, so the rate would decrease rather than increase.