Problem 6 - Campbell Biology

Question

If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? (A) Additional substrate will be formed. (B) The reaction will change from endergonic to exergonic. (C) The free energy of the system will change. (D) Nothing; the reaction will stay at equilibrium.

Step-by-Step Solution

Answer

D

Step 1: Understanding the Role of Enzymes

Enzymes function to lower the activation energy of a reaction, but they do not alter the equilibrium position of the reaction.

Step 2: Analyzing Each Option

Consider what each of the options suggests:(A) Additional substrate implies the reaction shifts backwards, which doesn't remain at equilibrium.(B) Changing the reaction type from endergonic to exergonic alters the inherent properties of the reaction, which enzymes cannot do.(C) Free energy change would mean a shift in Gibbs free energy, yet enzymes do not affect this change for the system at equilibrium.(D) Nothing implies the system remains unchanged at equilibrium, which aligns with the enzyme's role not affecting the equilibrium position.

Step 3: Making the Determination

Since enzymes only speed up the approach to equilibrium without changing the equilibrium position or free energy, the correct answer must only involve no change from the current equilibrium.

Key Concepts

Enzyme Function

Enzymes are biological catalysts that speed up chemical reactions in living organisms. Let's think of them as the helpers that make reactions happen faster.

They achieve this by lowering the activation energy, which is the energy required to start a reaction. However, it is crucial to note that enzymes do not change the overall equilibrium of a reaction.

Instead, they help the reaction reach equilibrium faster by making it easier for the reaction to overcome the energy hurdle. This means the equilibrium position, where the rates of the forward and reverse reactions are equal, remains unchanged.

Activation Energy

Every chemical reaction needs a certain amount of energy to initiate, known as activation energy.

Without this activation energy, the reactants would not have enough energy to transform into products. Enzymes come into play by lowering this energy barrier.

Imagine it like climbing a hill: without an enzyme, you need to climb a very tall hill (high activation energy) to reach the other side. With an enzyme, the hill is much smaller (lower activation energy), making the journey easier and faster.

This process allows reactions to proceed more quickly under the same conditions but does not affect where the balance point (equilibrium) of the reaction lies.

Chemical Equilibrium

Chemical equilibrium occurs when the rate of the forward reaction (substrate to product) equals the rate of the reverse reaction (product back to substrate). At this point, the concentrations of reactants and products remain constant over time.

Introducing an enzyme into this system doesn't change the balance point. The enzyme simply helps the system reach equilibrium more quickly.

In the original exercise, the question asked what happens if an enzyme is added to a reaction at equilibrium. The correct answer is that nothing will change because the equilibrium point itself remains the same.

Gibbs Free Energy

Gibbs free energy (often just 'free energy') is a thermodynamic property that can predict whether a reaction will occur spontaneously.

At equilibrium, the Gibbs free energy of the system is at its minimum, meaning there is no net change in the system. Enzymes do not alter Gibbs free energy; they only affect the rate at which equilibrium is reached.

If a reaction is already at equilibrium, adding an enzyme will not change the free energy or push the reaction to wherever the equilibrium lies.
To sum up, enzymes are crucial for accelerating reactions, but they do not change the fundamental properties like equilibrium positions and Gibbs free energy in a system at equilibrium.