Collision Theory
The rate of a reaction depends on two factors.
1) The number of collision per unit time between the reacting species.
2) The fraction of these collisions that are successful in producing a mew molecule.
 
Collision Geometry
If two or more molecules collide but are not orientated correctly then no reaction will take place.
 



 
For a reaction to occur, molecules must collide not only with sufficient energy but with the proper orientation.