Which of the following best explains the effects of a catalyst on the rate of a reversible reaction?

It provides a new reaction path with a lower activation energy

The correct answer is option 4. It provides a new reaction path with a lower activation energy.

Let us delve deeper into how a catalyst affects the rate of a reversible reaction by providing a new reaction path with a lower activation energy.

Understanding Catalysts and Activation Energy:

Catalyst Function:

A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy required for the reaction to proceed. It achieves this without being consumed in the reaction itself.

Activation Energy:

Activation energy (\( E_a \)) is the minimum energy required for a chemical reaction to occur. Molecules need to collide with enough energy to break bonds and form new ones to initiate a chemical change.

Effect of a Catalyst on Activation Energy:

When a catalyst is present in a reaction, it interacts with the reactants to form an intermediate species or complex. This intermediate lowers the activation energy required for the reaction to proceed. By providing an alternative reaction pathway with a lower activation energy barrier, the catalyst allows more reactant molecules to achieve the necessary energy to undergo the reaction. This lowering of activation energy speeds up both the forward and reverse reactions in a reversible reaction.

Reversible Reactions:

In a reversible reaction, reactants can form products, and products can also react to reform the reactants. The catalyst affects both directions of the reaction by lowering the activation energy for both processes. It does not change the equilibrium constant or the position of equilibrium but accelerates the attainment of equilibrium by enhancing the rates of both the forward and reverse reactions equally.

Why a Catalyst Provides a New Reaction Path with Lower Activation Energy:

Alternative Pathway: A catalyst alters the mechanism of a reaction by forming a new intermediate species or complex that reacts more readily than the original reactants alone.

Lower Activation Energy: By providing this alternative pathway, the catalyst reduces the activation energy barrier that molecules must overcome to undergo the reaction.

Increased Reaction Rate: With a lower activation energy, more molecules possess the necessary energy to react, resulting in an increased reaction rate.

Conclusion: The fundamental role of a catalyst in a reversible reaction is to provide a new reaction pathway with a lower activation energy. This enables the reaction to occur faster in both the forward and reverse directions, without changing the equilibrium position itself. This explanation encapsulates how a catalyst fundamentally influences the kinetics of chemical reactions.