Problem 24 - A Complete Resource Book in Chemistry for JEE Main

Question

In a reversible reaction, the catalyst (a) decreases activation energy of forward reaction (b) increases activation energy of forward reaction (c) decreases activation energy of both forward and backward reactions (d) increases activation energy of backward reaction

Step-by-Step Solution

Answer

(c) decreases activation energy of both forward and backward reactions.

Step 1: Understand the Role of a Catalyst

A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It achieves this by providing an alternate pathway for the reaction with a lower activation energy.

Step 2: Recognize the Nature of Reversible Reactions

In a reversible reaction, both the forward and backward reactions occur. The catalyst will affect both directions equally because it alters the activation energy barrier that both processes need to overcome.

Step 3: Analyze the Effect of the Catalyst

By definition, a catalyst decreases the activation energy required for a reaction to proceed. This effect applies to both the forward and backward reactions in a reversible process.

Step 4: Identify the Correct Option

Considering that the catalyst reduces the activation energy for both the forward and backward reactions without affecting the equilibrium, the correct choice is (c) decreases activation energy of both forward and backward reactions.

Key Concepts

Activation Energy Reduction

In chemical reactions, the concept of activation energy plays a crucial role. Activation energy refers to the minimum energy required to initiate a reaction. Think of it as the energy "hurdle" that reactants need to "jump over" to become products. Without overcoming this energy barrier, the reaction will not proceed.

A catalyst helps by lowering this activation energy. Imagine it acting as a shortcut on a road, making it easier for the reactants to convert into products.

• With reduced activation energy, more molecules have enough energy to undergo the reaction at a given temperature.
• This results in an increased reaction rate.
• Importantly, the catalyst itself remains unchanged and can be reused.

By lowering the activation energy, catalysts can dramatically increase the speed of reactions without being used up or permanently altering the chemical equilibrium of the system.

Role of Catalysts

Catalysts are vital in both industrial applications and biological systems. In a reaction, they offer an alternative pathway that requires less energy. This is essential in processes where energy savings are paramount. They speed up reactions that would otherwise be too slow to be practical.

In biological systems, enzymes act as catalysts. They enable vital bodily functions by rapidly facilitating biochemical reactions necessary for life.

• They provide efficiency, allowing processes to occur faster and with less energy.
• They can be specific, catalyzing only certain reactions.
• Importantly, they are not consumed in the reaction, allowing for repeated use.

The ability of catalysts to lower activation energy while remaining unchanged makes them indispensable in many fields, from manufacturing to healthcare.

Reversible Reactions

Reversible reactions are fascinating because they can proceed in both forward and reverse directions. This dynamic can be influenced by the presence of a catalyst. Importantly, catalysts reduce the activation energy for both the forward and backward reactions in these systems.

In simple terms, a reversible reaction can be visualized as a two-way street. A catalyst acts like an efficiency booster for vehicles traveling in both directions.

• It enables not just the forward reaction, where reactants form products, but also the reverse, where products revert to reactants.
• This dual action facilitates the establishment of chemical equilibrium, where both reactions occur at the same rate.
• By lowering energy barriers both ways, the catalyst ensures efficiency but does not disturb the equilibrium itself.

Understanding reversible reactions and the role catalysts play in them is critical for mastering concepts in chemical kinetics and thermodynamics.