Problem 87 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

For the following Assertion and Reason, the correct option is: Assertion: For hydrogenation reactions, the catalytic activity increases from Group 5 to Group 11 metals with maximum activity shown by Group \(7-9\) elements. Reason: The reactants are most strongly adsorbed on group \(7-9\) elements. (a) The assertion is true, but the reason is false. (b) Both assertion and reason are false. (c) Both assertion and reason are true and the reason is the correct explanation for the assertion. (d) Both assertion and reason are true but the reason is not the correct explanation for the assertion.

Step-by-Step Solution

Answer

(d) Both assertion and reason are true but the reason is not the correct explanation for the assertion.

Step 1: Analyzing the Assertion

The assertion claims that in hydrogenation reactions, catalytic activity increases from Group 5 to Group 11 metals, with peak activity in Group 7-9 elements. This is a well-established fact based on the electronic configuration and surface properties of transition metals in these groups, which facilitate catalytic activity. Thus, the assertion is true.

Step 2: Evaluating the Reason

The reason suggests that the reactants are most strongly adsorbed on Group 7-9 elements. Strong adsorption is crucial for catalytic activity, but if the adsorption is too strong, it could hinder the desorption of products, thereby reducing catalytic efficiency. Therefore, while adsorption is important, it should not be excessively strong.

Step 3: Comparing Assertion with Reason

The assertion talks about the catalytic activity, and the reason addresses adsorption strength. Even though adsorption is a factor influencing catalytic activity, the reason implies excessive adsorption, which does not perfectly explain the peak catalytic activity in Group 7-9 elements. Hence, the reason is not the correct explanation of the assertion.

Step 4: Conclusion on Correct Option

Both the assertion and the reason are true individually. However, the reason does not accurately explain why the assertion is true, since the relation between adsorption and catalytic activity does not align with excessive adsorption.

Key Concepts

Transition Metals

Transition metals are fascinating elements that lie in the middle of the periodic table. They include metals like Iron ( Fe ), Cobalt ( Co ), and Nickel ( Ni ). These metals are known for their ability to easily lose electrons and form different oxidation states.
Their unique electron configurations, which include a partially filled d -subshell, gives these metals some interesting properties, including being excellent catalysts. When it comes to catalytic activity, transition metals show a wide range of effectiveness. Catalysts are substances that speed up a chemical reaction without being consumed in the process. Transition metals can facilitate reactions like hydrogenation, where hydrogen is added to other molecules.

• Their multiple oxidation states allow them to transfer electrons readily.
• The partially filled d -orbitals provide available sites for reactions to occur.
• They can form complex structures with reactants, effectively lowering the energy barrier for the reaction.

Overall, these characteristics make transition metals essential in many industrial processes that require catalysts.

Adsorption

Adsorption is the process where molecules, atoms, or ions are held on the surface of a solid or liquid. An important factor in catalysis, this concept describes how reactants in a hydrogenation reaction gather on a metal catalyst's surface.
Effective adsorption ensures that reactants are sufficiently close to the catalyst to react. The challenge with adsorption is finding the "golden spot"—strong enough to attract reactants to the surface, but not so strong that products cannot leave.

• Optimally balanced adsorption supports more efficient catalytic cycles.
• Surface properties and electronic configurations of catalysts influence adsorption strength dramatically.
• For example, metals like those in Groups 7-9 often have the right balance for many reactions.

This delicate balance is key for maintaining high catalytic activity, as stronger adsorption isn't always better, given it can hinder reaction completion.

Group 7-9 Elements

The elements in Group 7-9 of the periodic table, including Manganese ( Mn ), Iron ( Fe ), and Cobalt ( Co ), are notable for their peak catalytic activity in certain reactions. These groups span transition metals that are optimally efficient for hydrogenation processes. Why do these groups shine in catalytic activity?

• They have the ideal electron configuration and surface properties to provide effective sites for adsorption.
• This balance fosters the "just right" adsorption strength needed to facilitate reactant interaction without preventing product desorption.
• Additionally, these metals hold a sweet spot in terms of varying electron availability, making them excellent at stabilizing reactive intermediates.

Consequently, Group 7-9 elements play a crucial role in both industrial and chemical synthesis reactions, harnessing their adsorption strengths to speed up reactions efficiently while ensuring completion.