In Chemistry, what is the Collision Theory?

In Chemistry, what is the Collision Theory?

In the field of Chemistry we can describe Collision Theory as the reactions or collisions when particles of certain reactant hit each other and then only a certain amount of collisions happen, not all and which results in some change. These changes that happen are known as successful collisions. The successful collisions should have enough energy to break the bonds that already exist between the particles and the form new bonds, The energy that they show to break those bonds is known as the activation energy. The new bonds will form the new products as a result of the successful reaction. The reactants are highly concentrated and hence this results in more successful reactant collision. When we increase the temperature then we have more kinetic energy of the molecules in the solution. This results in more kinetic energy being generated and hence the amount of collisions also increases. The Collision theory was first proposed by Max Trautz in the year 1916 and William Lewis in 1918.

The collision theory is very closely related to the field of Chemical kinetics. When we take a catalyst and it is involved in the collision of the reactant molecules we do require less amount of energy for the chemical change to take place and hence more of the collisions will have enough energy for the chemical reactions to occur. The rate of reaction also increases.

Let us consider the below:

X + Y ———> Z

In the Collision theory we will consider two particles X and Y and they will collide and if their nuclei gets closer than a particular distance. The area around the molecule X which will collie now with the approaching molecule Y is called the cross section of the reaction for X and Y. In very simple description we can say that the area which corresponds to the circle whose radius is actually the summation of the radii of both the reacting molecules i.e. X and Y is actually spherical.

The particular molecule which moves will take with it a certain amount of volume per second as it moves and therefore it can describe the average velocity of the particle. For example, if we take collision between solid balls. Here the molecules are quantum mechanised and hence many particles of the system of the electrons and the nuclei based on the certain interactions. Here the radius is related to the length of the interaction potential.

From the kinetic theory standpoint a certain molecule X will have an average velocity. When two body which are moving which have reduced masses for both the bodies and and the velocity of the mass centre. For a given molecule hence it travels before hitting another molecule if the hit molecule is fixed with no such movement where we have a an average travelling distance. Now the relative velocity can be calculated using the reduced mass of both the hitting molecules.

Now the collision theory for it to happen or be successful the reacting particles must :

1. Collide with each other and one another
2. The reacting particles must collide with enough energy
3. There must be proper orientation between them.

Properties for the Collision Theory.

1. There should be enough energy among the reacting particles
2. There must be a Collision or else there is no theory
3. They need to predict the rates of chemical reactions
4. Here the rate of reaction is proportional to the rate of the reactant collisions.
5. When the collision happens there must be an orientation between the atoms of the molecules which will be bonded together after the collision happens.
6. The rate of the reaction depends on the frequency of the collision.
7. Effective Collisions happen to result in a chemical reaction. Hence a certain amount of energy is required for this which is called as the activation energy.
8. The minimum energy required for a collision to happen is known as the threshold energy and hence if all the molecules which collide has energy less than the threshold energycannot produce successful collisions.

If we see the above diagram then we see the simple way it has been defined in the diagram that for any collision to happen then we need to have enough energy and there must be irritation and there must be a collision.

1. The Average effective collision cross section- This is defined as the area around a particle in which the centre of another particle must be in some sort of order for the collision to happen. This is the basic property of the collision theory and it happens to be the crux or foundation for any reacting molecule collision to happen.
2. Collisional Frequency is the average in which two reacting molecules collide for a given system and is used to express the average number of collisions per unit of time in a particular system.

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