Rate = Z * f * e^(-Ea/RT). Z = collision frequency (proportional to concentration and sqrt(T)). f = steric factor (orientation probability, typically 10^-1 to 10^-9). e^(-Ea/RT) = fraction of collisions with energy >= Ea. Effective collision = collision with (1) sufficient energy (>= Ea) AND (2) proper orientation. Most collisions are ineffective — only a tiny fraction leads to reaction. Increasing temperature increases the fraction of molecules with E >= Ea exponentially (Maxwell-Boltzmann distribution shifts right). Increasing concentration increases Z (more collisions per unit time). The steric factor explains why actual rates are lower than predicted by simple collision frequency — not all energetically sufficient collisions have the right geometry.