What is the central idea of collision theory in chemical kinetics?

• A. Reactions occur when molecules collide with sufficient energy and proper orientation; rate depends on collision frequency, energy, and orientation.
• B. Reactions occur only when catalysts are present.
• C. Temperature has no effect on collision frequency.
• D. Solvation shell controls rate independent of collisions.

Answer: (B)

Collision theory says that a reaction can occur only when reacting molecules meet by colliding with enough energy to get over the activation barrier and in a favorable orientation that allows bond breaking and forming. The rate of the reaction depends on how often these effective collisions happen, which is controlled by how often molecules collide (collision frequency) and how likely those collisions are to have both sufficient energy and proper alignment. Temperature plays a big role because higher temperature increases molecular speeds, raising both the number of collisions and the fraction with energy above the activation energy. A reaction does not require a catalyst to proceed—catalysts simply provide an alternative, lower-energy pathway that increases the fraction of effective collisions, but reactions can occur without them. Solvent effects and the surrounding environment can influence how readily particles approach each other and how energy is transferred during collisions, but the central driver remains the occurrence of effective collisions governed by energy and orientation.