# Collision Frequency Definition

The collision frequency is defined as the average rate at which two reactants collide in the given system. It is used for expressing the average number of collisions per unit time for a given system.

There are few assumptions that are made before calculating the collision frequency and they are:

• Molecules travelling through space are in straight lines.
• The shape of these molecules are spherical and are hard.
• Only two molecules react.
• For reaction to take place, the distance between these two molecules should either be less or equal to the sum of their respective radii.

Following is the equation used for collision frequency:

 $Z_{AB}=N_{A}N_{B}(r_{A}+r_{B})^{2}\sqrt{\frac{8\pi K_{B}T}{\mu _{AB}}}$