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: Understanding Activation Energy

Activation energy is the minimum energy required for a reaction to occur. Catalysts work by providing an alternative pathway with lower activation energy.

Step 2: Analyzing the Effect on Forward Reaction

A catalyst decreases the activation energy of the forward reaction. This is because it provides an alternative reaction pathway that requires less energy.

Step 3: Analyzing the Effect on Backward Reaction

Similarly, a catalyst also decreases the activation energy of the backward reaction. The alternative pathway provided by the catalyst applies to both the forward and backward reactions in a reversible reaction.

Step 4: Choosing the Correct Option

Option (c) 'decreases activation energy of both forward and backward reactions' is correct. A catalyst lowers the activation energy for both directions in a reversible reaction.

Key Concepts

Activation Energy

Understanding activation energy is key to grasping how chemical reactions proceed. Activation energy is the minimum amount of energy that reactant molecules need to collide effectively and transform into products.
This concept can be visualized as a barrier that reactants need to overcome to be transformed into products.

• Without enough energy, the molecules will simply bounce off each other.
• Once the activation energy barrier is crossed, the reaction proceeds.
• Lowering this energy barrier can make reactions occur faster and more efficiently.

Catalysts come into play by reducing this energy requirement. They do not change the overall energy of the reactants or products, instead they enable the reaction to occur more easily by offering a different path that requires less energy. This is often visualized as finding a new, easier path up a mountain, making the climb less strenuous.

Reversible Reactions

Reversible reactions are fascinating because they can proceed in both directions. Both the conversion of reactants to products and the conversion of products back into reactants can occur.

• At the molecular level, it's like a dance where molecules can change partners or take back former ones.
• Equilibrium is reached when the rates of the forward and backward reactions are equal.

The presence of a catalyst in a reversible reaction affects both the forward and backward reaction pathways. It not only accelerates how quickly a reaction reaches equilibrium but also ensures that both directions have a lower energy requirement. Thus, a catalyst can help maintain a dynamic balance between the reactants and products.

Reaction Pathways

Every chemical reaction follows a specific path from reactants to products, which is known as its reaction pathway. Some reactions happen spontaneously, but others require help to lower the activation energy.
Catalysts offer a new pathway by changing the mechanism or steps the reaction takes.

• This often involves forming temporary complexes between the catalyst and reactants.
• The key is that the alternative pathway requires less energy, making the reaction faster.
• Remember, catalysts are not consumed in the reaction; they are restored to their initial form when the reaction is complete.

In practical terms, choosing the right catalyst can significantly affect the efficiency and rate of industrial chemical processes, making it an invaluable tool in the field of chemistry.