Question

How do catalysts affect collision theory?

Answer 1

Hint: To determine the answer to this question we should know what collision theory is and what catalysts are. As the name indicates this theory tells the reaction starts by the collisions between the reactant molecules. By the collision, reactant molecules cross the energy barrier to form the product. Reaction time is the time required by the reactant molecules to convert into products molecules. The substances that increase the rate of reaction are known as catalysts.

Complete step by step answer:
First we will understand the collision theory and the factors on which the rate depends according to the Collision theory:
- The collision theory explains us about the rate of reaction means how fast or slow a reaction will be. The collision theory is mainly based upon the collisions between reacting molecules.
- According to collision theory, during a chemical reaction, the reactant molecules collide so their energy increases to cross over the energy barrier to form an activated complex and the product.

According to collision theory, the rate of the reaction depends upon three factors:
1. Collision frequency
2. Number of effective collisions
3. Fraction of molecules possessing the energy equal to greater than the activation energy.

So, we can write the rate constant of a reaction according to the collision theory as,
${\text{K}}\,{\text{ = }}\,{\text{PZ}}{{\text{e}}^{{{\text{E}}_{\text{a}}}{\text{/RT}}}}$
Where,
K is the rate constant
Z is the number of effective collision or collision frequency
${{\text{e}}^{{{\text{E}}_{\text{a}}}{\text{/RT}}}}$ is the Fraction of molecules possessing the energy equal to greater than the activation energy

So, the collision theory explains reaction times in terms of effective collision with proper orientations. If the collision frequency, the number of effective collisions with proper orientation are high then the rate of the reaction will be high.

Now, let’s understand what catalysts are:
Catalyst increases the rate of reaction by decreasing the activation energy. They decrease the activation energy by forming an intermediate complex with reactant which decomposes into products.

Therefore, the catalyst affects the activation energy only whereas the rate according to the collision theory depends upon the number of effective collisions, so the catalyst does not affect the collision theory.

Note: The catalyst does not reduce the rate of reaction. Catalyst does not change the Gibbs free energy of the reaction. Catalyst works on intermediate complex theory. Collision theory considered the molecules as a hard-sphere. The number of collisions per second and unit volume of the reaction medium is known as collision frequency. The energy required to form the activated complex is known as activation energy. All the collisions do not lead to the formation of an activated complex because all collisions do not have sufficient only those collisions in which molecules are in proper orientation lead to the energy of the molecule equal to the greater than the activation energy, cause the formation of the activated complex. These collisions which lead to the formation of the product are known as effective collisions and defined in terms of probability factor or steric factor.