The role of catalyst is to change:

Activation energy of the reaction

The correct answer is option 3. Activation energy of the reaction.

Let us delve into the details of each option and understand the role of a catalyst in more depth:

1. Gibbs Energy of Reaction

Gibbs free energy (\(\Delta G\)) is the measure of the spontaneity of a reaction. It combines the enthalpy change (\(\Delta H\)) and entropy change (\(\Delta S\)) of the reaction according to the formula \(\Delta G = \Delta H - T \Delta S\), where \(T\) is the temperature.

Catalyst Effect: A catalyst does not change the Gibbs free energy of the reaction. It accelerates the rate at which equilibrium is reached by lowering the activation energy but does not affect the energy difference between the reactants and products. Hence, the position of equilibrium or the spontaneity of the reaction is not altered by the catalyst.

2. Enthalpy of Reaction

Enthalpy change (\(\Delta H\)) is the total heat content of the system, and it represents the heat absorbed or released during the reaction at constant pressure.

Catalyst Effect: A catalyst does not alter the enthalpy change of a reaction. It only affects the rate of reaching equilibrium by providing an alternative reaction pathway with a lower activation energy. The total heat content of the system, therefore, remains unchanged.

3. Activation Energy of the Reaction

Activation energy (\(E_a\)) is the minimum energy required to initiate a chemical reaction. It is the energy barrier that reactants must overcome to be converted into products.

Catalyst Effect: A catalyst works by lowering the activation energy of the reaction. It provides an alternative pathway for the reaction that has a lower energy barrier. This means that more reactant molecules have sufficient energy to overcome this barrier, resulting in an increased reaction rate. The catalyst is not consumed in the reaction and can continue to facilitate the reaction.

4. Equilibrium Constant

The equilibrium constant (\(K\)) is a measure of the ratio of the concentrations of products to reactants at equilibrium. It is related to the Gibbs free energy change of the reaction by the equation \( \Delta G = -RT \ln K \), where \(R\) is the gas constant and \(T\) is the temperature.

Catalyst Effect: A catalyst does not change the equilibrium constant. It accelerates the rate at which equilibrium is reached but does not alter the position of equilibrium or the ratio of products to reactants at equilibrium. The equilibrium constant depends on the Gibbs free energy change, which is unaffected by the presence of a catalyst.

SummaryThe role of a catalyst is to lower the activation energy of a reaction, thereby increasing the rate at which equilibrium is achieved. It achieves this by providing an alternative reaction pathway with a lower energy barrier. However, it does not affect the Gibbs free energy, enthalpy, or equilibrium constant of the reaction. The correct answer to the question about the role of a catalyst is 3. Activation energy of the reaction.