Problem 1 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following is not an example of heterogeneous catalytic reaction?(a) Ostwald's process (b) Combustion of coal (c) Hydrogenatoin of vegetable oils (d) Haber's process

Step-by-Step Solution

Answer

Combustion of coal is not a heterogeneous catalytic reaction.

Step 1: Understand Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst that is in a different phase from the reactants. It often involves solid catalysts facilitating reactions between gaseous or liquid reactants.

Step 2: Identify the Nature of Reactions

Examine each option to determine whether it involves heterogeneous catalysis: - (a) Ostwald's process: Involves gases (NO, O2, and NH3) reacting over a solid platinum catalyst. - (b) Combustion of coal: Involves solid coal reacting directly with gaseous oxygen. - (c) Hydrogenation of vegetable oils: Involves liquid oils reacting with hydrogen gas in the presence of a solid nickel catalyst. - (d) Haber's process: Gaseous reactants (N2 and H2) interact over a solid iron catalyst.

Step 3: Determine the Reaction Without a Catalyst

Identify which process does not clearly involve a heterogeneous catalyst: - While Ostwald's, Haber's, and hydrogenation processes explicitly use solid catalysts to interact with gas or liquid phase reactants, combustion of coal does not typically involve a distinct catalyst but rather a direct reaction with oxygen.

Step 4: Conclusion

Conclude which process does not typically involve heterogeneous catalysis: combustion of coal typically proceeds through direct interaction between the solid fuel and gaseous oxygen without an additional catalyst.

Key Concepts

Ostwald's Process

Ostwald's Process is a crucial chemical procedure used in the production of nitric acid, which is an essential industrial chemical. The process involves the reaction of ammonia (\( \text{NH}_3 \)) with oxygen (\( \text{O}_2 \)) to form nitric oxide (\( \text{NO} \)), nitrogen dioxide (\( \text{NO}_2 \)), and finally, nitric acid (\( \text{HNO}_3 \)). A solid platinum-rhodium catalyst facilitates this conversion, which qualifies it as a heterogeneous catalysis process.
This method consists of multiple steps:

• Ammonia combustion: \( 4 \text{NH}_3 + 5 \text{O}_2 \rightarrow 4 \text{NO} + 6 \text{H}_2\text{O} \)
• Oxidation of nitric oxide to nitrogen dioxide: \( 2 \text{NO} + \text{O}_2 \rightarrow 2 \text{NO}_2 \)
• Absorption of nitrogen dioxide in water to form nitric acid: \( 3 \text{NO}_2 + \text{H}_2\text{O} \rightarrow 2 \text{HNO}_3 + \text{NO} \)

Each reaction step benefits significantly from the use of a solid platinum catalyst, ensuring higher yields and efficiency. This process is widely adopted in the production of fertilizers and explosives.

Haber's Process

Haber’s Process is essential for synthesizing ammonia, a key ingredient in fertilizers. This process revolutionized agriculture by making synthesized ammonia easily accessible. It involves a reaction between nitrogen gas (\( \text{N}_2 \)) and hydrogen gas (\( \text{H}_2 \)) to produce ammonia (\( \text{NH}_3 \)) over an iron catalyst.
The chemical equation for this synthesis is: \[ \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 \]Some characteristics that define this process include:

• Operates under high pressure, typically around 200 atm, to maximize yields.
• Operates at high temperatures, approximately 450-500 °C.
• Utilizes a finely divided iron catalyst, often promoted with traces of potassium oxide and aluminum oxide, to enhance activity.

This method offers a way to convert atmospheric nitrogen into ammonia, fulfilling a significant portion of the world's nitrogen fertilizer needs and making it vital to global food production.

Hydrogenation of Oils

Hydrogenation of Oils refers to the process of adding hydrogen to unsaturated bonds in vegetable oils, converting liquid oils into solid or semi-solid fats. This reaction is widely used in the food industry to produce margarine and shortening from vegetable oils.
The typical hydrogenation process involves:

• The presence of a nickel catalyst that accelerates the reaction.
• Applying moderate pressure and temperatures to facilitate the hydrogenation process.
• The reaction typically occurs as: \[ \text{C}_n\text{H}_{2n} + \text{H}_2 \rightarrow \text{C}_n\text{H}_{2n+2} \]

One of the significant benefits of this process is the increase in the shelf life and stability of the oils.
However, partial hydrogenation can result in trans fats, which have health concerns. Hence, the process must be carefully controlled to produce the desired product profile while minimizing undesirable trans fat formation.