Collision theory, activation energy and catalysts

Collision theory, activation energy and catalysts

Collision theory explains rate at particle level. Particles must collide, collide often enough, have energy at least equal to activation energy and have appropriate orientation for bonds to rearrange. A catalyst provides an alternative pathway with lower activation energy, increasing the fraction of collisions that are effective at the same temperature. It is not consumed overall and does not alter the energy difference between reactants and products. Increasing concentration increases collision frequency in solution; increasing surface area exposes more solid particles; increasing temperature changes both collision frequency and energy distribution.

Work it through

Two identical reactions are compared at the same concentration. One uses a catalyst and finishes sooner. The catalyst did not supply reactant particles or make the reaction more exothermic; it lowered the energy barrier. On an energy profile, draw a lower peak but keep reactant and product levels unchanged.

Mastery target

Use collision theory to explain rate factors, distinguish activation energy from enthalpy change and interpret the role of a catalyst in an experiment or energy profile.