collision theory
Theory of chemical reactivity that states that only colliding molecules can undergo chemical reaction and then only if their combined kinetic energy exceeds a critical value.
The maximum value for the rate coefficient for a simple, bimolecular, gas-phase reaction, assuming reaction occurs on every collision, is about 2 × 10-10 cm3 per molecule per second. Actual rate coefficients are lower due to two effects—the need to overcome an energy barrier during collision in order for reaction to occur, and a “steric factor,” which accounts for the fact that reaction can occur only when the collision occurs in a certain geometry.