Question

Which is not an example of homogeneous catalyst? (a) Formation of \(\mathrm{SO}_{3}\) in chamber process (b) Formation of \(\mathrm{SO}_{3}\) contact process (c) Hydrolysis of methyl acetate in the presence of an acid (d) Decomposition of \(\mathrm{KClO}_{3}\) in the presence of \(\mathrm{MnO}_{2}\)

Short answer

The answer is (b) Formation of \(\mathrm{SO}_{3}\) contact process. \(\mathrm{SO}_{2}\) is oxidized to \(\mathrm{SO}_{3}\) in the presence of \(\mathrm{V}_{2}\mathrm{O}_{5}\). The catalyst (\(\mathrm{V}_{2}\mathrm{O}_{5}\)) is solid while the reactants and products are gases, hence this an example of heterogeneous catalysis and not homogeneous catalysis.

Step-by-step solution

Analyzing Option (a)

Formation of \(\mathrm{SO}_{3}\) in chamber process: In this process, \(\mathrm{SO}_{2}\) and \(\mathrm{O}_{2}\) gas react to form \(\mathrm{SO}_{3}\) gas in the presence of nitrogen oxides which act as a homogeneous catalyst because they are all in the same phase (gas). So, it is an example of homogeneous catalysis.

Analyzing Option (b)

Formation of \(\mathrm{SO}_{3}\) contact process: In this process, \(\mathrm{SO}_{2}\) is oxidized to \(\mathrm{SO}_{3}\) in the presence of \(\mathrm{V}_{2}\mathrm{O}_{5}\). The catalyst (\(\mathrm{V}_{2}\mathrm{O}_{5}\)) is solid while the reactants and products are gases, hence this an example of heterogeneous catalysis and not homogeneous catalysis.

Analyzing Option (c)

Hydrolysis of methyl acetate in the presence of an acid: In this reaction, the reactant (methyl acetate), the product (methanol and acetic acid) and the catalyst (an acid) are all in the same phase (liquid). Hence, this is an example of homogeneous catalysis.

Analyzing Option (d)

Decomposition of \(\mathrm{KClO}_{3}\) in the presence of \(\mathrm{MnO}_{2}\): In this process, \(\mathrm{KClO}_{3}\), a solid, decomposes in the presence of a solid catalyst, \(\mathrm{MnO}_{2}\), to produce \(\mathrm{KCl}\) and \(\mathrm{O}_{2}\). Hence, this is an example of homogeneous catalysis.

Key concepts

Homogeneous Catalysis

In homogeneous catalysis, the catalyst and the reactants are in the same phase, typically in a gaseous or liquid state. This similarity helps in easy interaction between the catalyst and the reactant molecules.
Homogeneous catalysis is predominately used in chemical processes involving liquids where both reactants and catalysts mix easily. For example, in the hydrolysis of methyl acetate in the presence of an acid, both the reactant and the acid catalyst are in a liquid state.
Some advantages of homogeneous catalysis include:

• Uniform mixture and reaction conditions.
• Easy to control the reaction environment.
• Effective at lower temperatures compared to heterogeneous reactions.

An example from the exercise is the formation of sulfur trioxide (\(\mathrm{SO}_{3}\)) in a chamber process, where all participating substances, including the catalysts, are gases.

Heterogeneous Catalysis

Heterogeneous catalysis involves catalysts that are in a different phase compared to the reactants. This often means that the catalyst is solid, and the reactants are gaseous or liquid.
Heterogeneous catalysts provide a surface upon which the reactants can adsorb, interact, and convert into products. This surface acts as a mediator and aids in the breaking and forming of chemical bonds.
Here are some key benefits of heterogeneous catalysis:

• Easy to separate the catalyst from the reaction mixture.
• High thermal stability, allowing use in high-temperature reactions.
• Useful in continuous processes.

An example of heterogeneous catalysis is the use of \(\mathrm{V}_{2}\mathrm{O}_{5}\) in the contact process to form \(\mathrm{SO}_{3}\), where the solid catalyst helps convert gaseous reactants.

Chemical Reactions

Chemical reactions involve the transformation of reactants into products through the breaking and forming of chemical bonds. Catalysts play a crucial role in many reactions, as they lower the activation energy needed to initiate the reaction.
Both homogeneous and heterogeneous catalysis have their applications based on the specific requirements of the reaction. Whether the catalyst is in the same medium as the reactants or different, its purpose remains consistent: to speed up the reaction.
Key points about chemical reactions with catalysts:

• Catalysts remain unchanged at the end of the reaction.
• They do not affect the equilibrium state but help reach it faster.
• Catalysts can be designed to be highly specific for certain reaction paths.

Understanding how each of these catalytic systems works helps grasp the overall dynamics of chemical transformations. This knowledge can be beneficial in industrial applications, environmental processing, and even biochemical reactions in the body.