Which change can increase the frequency of productive collisions by altering the phase of reacting species?

• A. Increase in temperature
• B. Increase in concentration
• C. Change to a more favorable state of matter
• D. Addition of a catalyst

Answer: (C)

Phase controls how freely reacting particles move and meet each other. When reactants shift to a more fluid or less rigid state, they can mix and collide more often, and with a better chance of orienting correctly for a reaction. This increase in the frequency of encounters that can lead to products is why changing to a more favorable state of matter boosts productive collision frequency.

Other factors can raise reaction rate, but they do so through different means: raising temperature increases kinetic energy and can help overcome the activation barrier; increasing concentration raises how often particles collide but doesn’t change the phase; a catalyst provides an alternate pathway with a lower activation energy rather than increasing the collision frequency through phase change.