Explain the intermediate complex formation theory of catalysis?

In this blog post you will learn about the intermediate complex formation theory of catalysis, or simply “theory of catalysis”.

I have explained everything in a best way to learn for exams. Stop youtube, stop facebook, stop netflix for the next 3 minutes. Take your pen and a rough copy. Then write the main points you read here in you own words. Then you are free to do whatever you like to do( I will recommend studying hard).

(Q) What is meant by catalysis? Point out its importance. Discuss intermediate compound formation theory of catalysis.

Catalyst is a substance which can make a difference or alter the current rate of reaction.

For e.g.-:

N2+3H2  =>2NH3

The types of catalysis are as follows-:

  1. Homogenous catalysis
  2. Heterogeneous catalysis
  3. Auto catalysis

Intermediate complex formation theory-:

Generally homogenous catalysis follows intermediate compound formation theory of catalysis.


Step 1-: the reactant reacts with the catalysis to form the intermediate complex.


A+C -> AC*(intermediate complex)

Step 2-: if that highly reactive intermediate complex reacts with another molecule, then it forms the product and regenerates the catalyst.

AC*+B -> AB+C

What actually happened here, is that due to the intermediate complex formation, activation energy decreases and rate of reaction accelerates.

The above figure shows the graph of catalysis reaction for the homogenous theory of catalysis.

(Q)What is heterogeneous catalysis? Giving a suitable example, explain the mechanism of heterogeneous catalysis. Write any 2 criteria for choosing a catalyst for industrial purpose.

Heterogeneous catalysis is such a catalysis where physical state of reactants and products is different.

SO2+O2→ SO3(in presence of V2O5


Adsorption theory of catalysis-:

This theory of catalysis is mainly applicable for heterogeneous catalysis. If the reactant is in gaseous phase and catalyst in solid state, then adsorption theory of catalysis comes into application.

For eg-:

A2+B2 → 2AB

These reactions occur in 4 steps-:

  1. First of all, all the reactants molecules get adsorbed on the surface of catalyst by weak forces of attraction( Van Der Waal’s Forces).
  2. Transition state is formed in between reactant molecules where existing bond starts to break, and new bond start to form as shown in below figure.
  3. Now adsorbed product is formed.
  4. Finally product molecule de-adsorb from the surface catalyst.


Now, I have given all the theories for both theory of catalysis, so you point out the differences between homogenous and heterogeneous catalysis.

Criteria for choosing catalysis for industrial applications-:

  1. It should be able to produce desired product as a major product.
  2. It should be efficient to produce the desired product.
  3. There should be easy method for the regeneration of catalyst.
  4. It should be cheap and easily available.
  5. It should be stable at normal condition.

Read more tutorials about chemistry-:

Chemistry Tutorials

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