Question

REFLECT AND APPLY Does the presence of a catalyst alter the standard free energy change of a chemical reaction?

Short answer

No, a catalyst does not alter the standard free energy change (ΔG°) of a chemical reaction.

Step-by-step solution

Understand the Question

The question asks whether a catalyst affects the standard free energy change (ΔG°) of a chemical reaction.

Define Standard Free Energy Change

Standard free energy change, denoted as ΔG°, is the change in free energy of a reaction under standard conditions (1 M concentration, 1 atm pressure, 298 K temperature). It determines the spontaneity of the reaction.

Define Catalyst

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It lowers the activation energy (Ea) required for the reaction to proceed.

Analyze the Effect of Catalyst on ΔG°

A catalyst accelerates the rate of the reaction by providing an alternative pathway with a lower activation energy. However, it does not affect the overall thermodynamics of the reaction, including the standard free energy change (ΔG°). Therefore, the presence of a catalyst does not alter the value of ΔG°.

Conclude

Conclude that while a catalyst speeds up the reaction rate, it does not change the standard free energy change of the reaction.

Key concepts

Standard Free Energy Change

Standard Free Energy Change, represented as \( \Delta G^\circ \), is an important concept in chemistry. It refers to the change in free energy of a reaction when it occurs under standard conditions: 1 M concentration, 1 atm pressure, and 298 K temperature. This value tells us which direction a reaction will spontaneously proceed. If \( \Delta G^\circ \) is negative, it indicates that the reaction will proceed spontaneously. On the other hand, a positive \( \Delta G^\circ \) means the reaction is non-spontaneous. A catalyst does not alter this value because \( \Delta G^\circ \) depends solely on the properties and quantities of the reactants and products.

Activation Energy

The Activation Energy (Ea) is the minimum energy required for a chemical reaction to occur. It's the 'energy barrier' that reactants must overcome to form products. A catalyst lowers this activation energy by providing an alternative pathway for the reaction. This means the reaction can take place more quickly and easily. However, it's important to understand that while a catalyst affects the speed of the reaction by lowering the Ea, it does not change the starting and ending energy levels of the reaction. Therefore, the standard free energy change (\( \Delta G^\circ \)) remains unaffected.

Reaction Rate

The Reaction Rate is a measure of how quickly the reactants in a chemical reaction are transformed into products. Various factors can influence the reaction rate, including temperature, concentration of reactants, and the presence of a catalyst. A catalyst specifically functions by speeding up the reaction rate without being consumed in the process. By lowering the activation energy, more reactants have the necessary energy to undergo the transformation at a given temperature. This results in a faster reaction. Despite this increase in speed, the overall energy change \( \Delta G^\circ \) of the reaction does not change, as it remains determined by the inherent thermodynamic properties of the reactants and products.

Enzyme Catalysis

Enzyme Catalysis is a specific type of catalysis carried out by biological molecules called enzymes. Enzymes accelerate reactions in living organisms to efficiently support life processes. Much like chemical catalysts, enzymes lower the activation energy required for reactions. They do this by binding to substrate molecules and stabilizing the transition state, making it easier to reach this state. As with non-biological catalysts, enzymes do not change the \( \Delta G^\circ \) of the reactions they regulate. They only make the reactions proceed faster. Enzymes themselves remain unchanged after the reaction and can be used repeatedly.