Which of the following statements is incorrect with respect to the use of a catalyst in the reversible reaction?

The catalyst increases the rate of only the forward reaction

The correct answer is option 1. The catalyst increases the rate of only the forward reaction.

Let us delve into how a catalyst functions in a reversible reaction and analyze each statement carefully:

Catalysts in Reversible Reactions

A reversible reaction is one where the reactants can convert to products, and the products can also convert back to reactants. The reaction can proceed in both directions—forward and backward—until it reaches equilibrium. A catalyst is a substance that speeds up the rate of a reaction without being consumed in the process. It achieves this by providing an alternative pathway for the reaction, one that has a lower activation energy compared to the uncatalyzed pathway.

Detailed Analysis of the Statements

1. The catalyst increases the rate of only the forward reaction:

This statement is incorrect. In a reversible reaction, a catalyst does not favor one direction over the other. It increases the rate of both the forward and backward reactions equally. The reason for this is that the catalyst lowers the activation energy for both the forward and reverse reactions, enabling both to proceed faster. By increasing the rates of both reactions, the catalyst helps the system reach equilibrium more quickly, but it does not affect the position of the equilibrium itself. Thus, the rates of both the forward and backward reactions are enhanced, not just one.

2. The catalyst increases the rate of both the forward and the backward reaction:

This statement is correct. A catalyst works by lowering the activation energy barrier for the reaction pathway, thereby increasing the reaction rates in both directions—forward and backward. This means that both the forward reaction (where reactants convert to products) and the backward reaction (where products revert to reactants) occur more quickly in the presence of a catalyst. The equilibrium is achieved faster, but the position of the equilibrium (the ratio of products to reactants at equilibrium) remains unchanged.

3. The catalyst decreases the activation energy of the overall reaction:

This statement is correct. The primary role of a catalyst is to lower the activation energy required for the reaction to occur. By providing an alternative reaction pathway with a lower activation energy, the catalyst increases the number of reactant molecules that have sufficient energy to overcome this barrier and convert to products. This applies to both the forward and backward reactions in a reversible reaction, leading to an increase in the rates of both reactions.

4. The catalyst itself does not undergo any chemical change:

This statement is correct. A true catalyst is not consumed or permanently altered in the reaction. While it may participate in intermediate steps of the reaction, it is regenerated in its original form by the end of the reaction cycle. This property allows the catalyst to be used repeatedly in multiple reaction cycles. The catalyst facilitates the reaction but remains unchanged in terms of its chemical composition and properties.

Conclusion
The statement that is incorrect is: option 1: The catalyst increases the rate of only the forward reaction.

This is incorrect because a catalyst increases the rates of both the forward and backward reactions equally in a reversible reaction, not just one direction.