Collision Frequency
Collision Frequency is the number of collisions per second per unit volume of the reacting mixture. It is commonly represented by the letter Z.
We already know that the rate of a chemical reaction is affected by Activation Energy, hence, we will establish a relation between the Rate of Reaction, Collision Frequency, and the Activation Energy of a chemical reaction. Consider the following reaction:
P + Q → Product
According to Collision Theory, the Rate of the above reaction is given by:
Rate = ZPQe−Ea/RT
Where,
- ZPQ is collision frequency of reactants P and Q
- Ea is Activation Energy
- R is Universal Gas Constant
- T is Temperature in absolute scale
If we compare the above equation with Arrhenius’s Equation k = A -Ea/RT we find that A which is the Pre-Exponential Factor in Arrhenius’s equation is similar to ZPQ i.e. Collision Frequency.
Effective Collision
In real scenario especially in the case of complex reaction, not all collision leads to the formation of a product. In order to form a product the collision of molecules must have minimum or sufficient kinetic energy and should also have proper orientation. Such a collision of molecules in which there is minimum energy and proper orientation that leads to the breaking and formation of a bond is called an Effective Collision.
To take account of effective collisions out of total collisions we have a factor ρ which is called the steric factor or the probability factor. Hence, the above equation for the Rate of Reaction can be rewritten as
Rate = ρZPQe−Ea/RT
Thus, we can say that Activation Energy and Proper Orientation are the two most important factors in determining Effective Collision and hence, the Rate of Reaction.
Apart from the above two mentioned factors, the surface area also impacts collision and rate of reaction. We will see its mechanism below:
Collision Theory: Surface Area
When the surface area is large, more molecules are present, and more molecules can react with each other, resulting in a higher collision or reaction rate. As a result, the larger the surface area, the faster the response. Furthermore, according to the collision hypothesis, if the surface area of molecules is greater, it has more energy and boosts the reaction rates.
Since not all collisions lead to the formation of new products based on this collision is classified into two categories. We will learn those types below.
Collision Theory
Collision Theory says that when particles collide (strike) each other, a chemical reaction occurs. However, this is necessary but may not be a sufficient condition for the chemical reaction. The collision of molecules must be sufficient to produce the desired products following the chemical reaction. The effective collision process, on the other hand, will determine the qualities and properties of the resulting product. As a result, understanding the collision theory is required in order to understand and determine the resulting products.
Max Trautz and William Lewis created the Collision Theory of Chemical Reactions in 1916-1918, which was based on the kinetic theory of gases. The kinetic Theory of Gases explains the behavior of gases by imagining them as a swarm of particles, molecules, or atoms moving in random directions.