What is Catalysis?
All reactants need to overcome certain energy, better known as activation energy in order to form products. This activation energy is the difference between the energy of transition state and the reactant species. Some reactant molecules have enough kinetic energy to overcome this energy barrier whereas others don’t.
Hence, not all the reactions happen at the same rate in general conditions. Therefore, certain reagents are added which lower the required activation energy for the conversion of reactants to products. These reagents are known as catalysts and this process of lowering the activation energy is known as catalysis.
Catalysis of chemical reactions increases the rate of chemical reaction with the help of a catalyst. Catalysts increase the rate of a reaction without undergoing any chemical or physical change. As discussed above, catalysts just decrease the energy barrier for the conversion of reactants to products.
Types of catalysis
Catalysis of chemical reactions is generally divided into two categories:
Homogeneous Catalysis: Homogeneous catalysis of chemical reactions is a process where the reactants involved in the reaction and the catalyst are in the same phase. For example hydrolysis of sugar in the presence of sulphuric acid.
Heterogeneous Catalysis: Heterogeneous catalysis of chemical reactions is a process where the reactants involved in the reaction and the catalyst are in different phases. For example reaction of hydrogen and nitrogen in the presence of finely divided iron to form ammonia.
Mechanism of Heterogeneous Catalysis of Chemical Reactions:
The modern theory of adsorption proposed a five-step mechanism for the catalysis of chemical reactions. These steps are:
- Introduction and diffusion of reactant molecules on the catalytic surface.
- Adsorption of molecules of reactants on the catalytic surface.
- Formation of intermediate on a catalytic surface by a chemical reaction between the reactant molecules.
- Desorption of product molecules from the catalytic.
- Diffusion of product molecules away from the catalytic surface to form final products.
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