What is collision frequency?

Collision frequency, used in chemical kinetics, measures the average number of collisions over time within a defined system. A collision occurs when two reactants collide in a system.

A few assumptions must be met to calculate collision frequency: Molecules travel in a straight line, are hard and solid spheres, the reaction being calculated only occurs between two molecules, and collisions are only measured as hit or miss. To calculate the collision frequency in a system, one must consider all except one molecule in a sample to be a fixed value. The speed of the one molecule is calculated relative to all of the other molecules.