Question

The reaction in which the reactant and the catalyst have one phase is__________________.
A) Heterogeneous catalysis
B) Homogenous catalysis
C) Solid-state catalysis
D) Solution catalysis

Answer 1

A catalyst is a substance which alters the rate of a chemical reaction without itself undergoing any change in mass and chemical composition is called a catalyst. There are two main types of catalysts. These are classified based on their phases with reactant and product.
i) Homogeneous catalyst
ii) Heterogeneous catalyst

Complete Solution :
When a catalyst is present in the same phase as the reactant and products it is called as a homogeneous catalyst. In these reactions, the catalyst, reactant, and products are in the same phase and are called homogeneous catalytic reactions or homogeneous catalysis.
For example:

1. In the lead chamber process, sulphur dioxide $\text{ S}{{\text{O}}_{\text{2 }}}$ is oxidized to $\text{ S}{{\text{O}}_{\text{3 }}}$ in the presence of nitric oxide as a catalyst:
   $\text{ 2 S}{{\text{O}}_{\text{2 }}}(g)+{{\text{O}}_{\text{2}}}\xrightarrow{\text{NO(g)}}\text{ 2 S}{{\text{O}}_{\text{3 }}}(g)\text{ }$
   The combination of $\text{ S}{{\text{O}}_{\text{2 }}}$ and $\text{ }{{\text{O}}_{\text{2 }}}$ is a slow process. However, in the presence of $\text{ NO }$(catalyst), the reaction becomes fast. Here, all reactants $\text{ S}{{\text{O}}_{\text{2 }}}$, products $\text{ S}{{\text{O}}_{\text{3 }}}$, and catalysts $\text{ NO }$ are in the gaseous phase.

2. Catalytic decomposition of ozone in the presence of $\text{ NO }$ or $\text{ Cl }$ atoms as a catalyst in the gas phase:
   $\text{ }{{\text{O}}_{\text{3}}}\text{+ O }\xrightarrow{\text{Cl(g) / NO (g)}}\,\text{2}{{\text{O}}_{\text{2}}}\text{ }$
   - The homogeneous catalytic reactions can be explained based on intermediate compound formation. According to this theory, the catalyst combines with one of the reactants to form an intermediate. The intermediate compound being unstable either decomposes or combines with the other reactant to form product and catalyst regenerated.
   Therefore, the reaction in which the reactant and the catalyst have one phase is homogeneous catalysis.

So, the correct answer is “Option B”.

Note:

Advantages of homogeneous catalysis:
i) Homogeneous catalysts are more selective than heterogeneous catalysts.
ii) This catalyst is easy to characterize so the reaction mechanism can be manipulated.
Disadvantages are as follows:
i) Separation of homogeneous catalysts from reaction mixture is a difficult task.
ii) They have limited thermal stability.