According to collision theory, which conditions must be satisfied for a reaction to occur?

• A. The particles must collide with the appropriate orientation and sufficient energy.
• B. The reaction rate is dictated only by temperature.
• C. A catalyst is always required for a reaction.
• D. Reactants must be in the same phase.

Answer: (A)

Collision theory says a reaction happens only when particles collide in a way that can lead to bonds breaking and forming. That requires two things at once: enough energy to overcome the activation barrier, and a favorable orientation so the reacting parts align to form the products. If the energy is too low, the collision just bounces apart; if the orientation is wrong, even a high-energy collision won’t produce products. Temperature, concentration, and surface area influence how often such effective collisions occur, but the essential conditions are both sufficient energy and proper orientation. Catalysts can help by providing a different pathway with a lower activation energy, but they are not required for all reactions. Reactants can react in the same phase or across different phases, so phase alone isn’t a universal constraint.