Collision theory is applicable only to bimolecular reactions mostly gases where the reactant molecules are considered as hard spheres that must collide with sufficient threshold energy and must be correctly oriented for the collision to be effective that results in the product formation.
The rate of the reaction, therefore, depends on the collision frequency, threshold energy, and the orientation (steric/probability) factor.
k= PZABe-Ea/RT
where,
P- Steric Factor
ZAB - Collision Frequency
Ea - Activation energy
R - Gas Constant
T - Temperature