Problem 73 - A Complete Resource Book in Chemistry for JEE Main

Question

In the reaction \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \stackrel{\mathrm{Dil} \cdot \mathrm{H}_{2} \mathrm{SO}}{\mathrm{H}}-\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})\) \(+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})\) dilute \(\mathrm{H}_{2} \mathrm{SO}_{4}\) acts as (a) homogeneous catalyst (b) heterogenous catalyst (c) heterogeneous reactant (d) homogeneous reactant

Step-by-Step Solution

Answer

(a) homogeneous catalyst

Step 1: Recognize the Problem Type

The problem is asking us to identify the role of dilute \( \mathrm{H}_2\mathrm{SO}_4 \) in the given chemical reaction.

Step 2: Understand the Reaction

Examine the reaction, which involves \( \mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \) reacting with \( \mathrm{H}_2 \mathrm{O} \) in the presence of dilute \( \mathrm{H}_2\mathrm{SO}_4 \) to form \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \) and another \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} \).

Step 3: Determine the Role of H2SO4

In this reaction, dilute \( \mathrm{H}_2\mathrm{SO}_4 \) is used to facilitate the reaction without being consumed in the process. It serves to accelerate the reaction and can be recovered unchanged at the end.

Step 4: Identify the Type of Catalyst

According to the definition, a homogeneous catalyst is in the same phase as the reactants, while a heterogeneous catalyst is in a different phase. Since both the reactants and dilute \( \mathrm{H}_2\mathrm{SO}_4 \) are in the liquid phase, it is a homogeneous catalyst.

Key Concepts

Understanding Homogeneous Catalysts

In chemistry, a **homogeneous catalyst** refers to a catalyst that operates in the same phase as the reactants involved in a chemical reaction. For example, if the reactants and the catalyst are all in the liquid phase, then the catalyst is considered homogeneous. This type of catalysis is essential for facilitating reactions without being consumed in the process, as seen in the given exercise involving sucrose hydrolysis. Here, dilute \(\mathrm{H}_2\mathrm{SO}_4\) acts as a homogeneous catalyst because it is in the same phase (liquid) as the reactants \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) and \(\mathrm{H}_2 \mathrm{O}\). The advantages of homogeneous catalysts include their ability to be well-dispersed in the reaction mixture and to provide a large contact area with the reactants. Moreover, they can often be more easily controlled, offering more precise reaction conditions.
When studying reactions involving homogeneous catalysis, students should pay attention to the states of matter of both reactants and catalysts and consider how this alignment impacts the effectiveness and efficiency of the chemical process.

Exploring Reaction Kinetics

**Reaction kinetics** is the study of the speed or rate at which chemical reactions occur and the factors that influence these rates. The kinetics of a reaction are crucial to understand because they reveal the steps and pathways through which reactants transform into products. In the context of the given exercise, the presence of a catalyst like \(\mathrm{H}_2\mathrm{SO}_4\) impacts these kinetics tremendously.

• The rate of reaction can be influenced by several factors including concentration, temperature, presence of a catalyst, and the physical state of reactants.
• In our reaction, dilute \(\mathrm{H}_2\mathrm{SO}_4\) increases the rate of hydrolysis of sucrose by providing a pathway with lower activation energy. This makes it easier for reactants to turn into products.

By lowering the activation energy, the catalyst allows more molecules to have enough energy to undergo the reaction, thus speeding up the process. Understanding reaction kinetics not only helps in predicting how fast a reaction will occur but also in designing industrial processes and understanding biological systems.

The Essential Role of Catalysts in Reactions

Catalysts play a pivotal role in many chemical reactions by significantly accelerating the rate at which reactions occur without being consumed themselves. In the exercise provided, we see how dilute \(\mathrm{H}_2\mathrm{SO}_4\) acts as a catalyst in the hydrolysis of sucrose. Here's how catalysts generally influence reactions:

• **Acceleration of Reaction Rates:** They offer an alternative reaction pathway with lower activation energy, increasing the number of collisions that lead to a successful reaction.
• **Efficiency:** Catalysts bring together reactants in a favorable position and provide an ideal environment for the reaction.
• **Selectivity:** They can increase the selectivity towards a desired product in complex reactions.

Moreover, because catalysts are not consumed, they can be used repeatedly. This characteristic makes them very valuable, particularly in industrial and environmental processes. By understanding the role of catalysts, students can better comprehend how various reactions can be fine-tuned and optimized to achieve desired results in both lab scale and industrial applications.