The collision theory plays a vital role in the study of chemical reactions and their kinetics. The behaviour of gases, atoms and molecules can be studied based on this theory.
What is collision theory?
According to the collision theory, “the molecules of reactants are assumed to be hard spheres and the reactions are assumed to occur only when these spheres (molecules) collide with each other”.
Hence, it was mandatory to identify the number of collisions occurring in order to form products so that we can have a clear picture of the reaction.
Drawbacks of collision theory
Every theory has certain limitations and drawbacks. This theory also had some of them. The following are the drawbacks of collision theory.
- This theory does not advance any explanation for the abnormally high rates that are observed sometimes.
- This theory cannot be applied to reversible reactions with complete success.
- It does not take into account the fact that proper molecule orientation is the requirement for a chemical reaction to occur. Active collision does not occur due to lack of proper orientation and therefore the experimentally observed frequency is less than determined based on the theory of collision.
- The theory of collision states that the reaction frequency is proportional to the total number of collisions per cc per second.
- It does not take into account the fast reactions where reactant molecules react despite having much less energy than the activation energy. These reactions are described by quantum mechanics, which means the reaction happens as a result of electrons being exchanged between reactant molecules.