Podcast
Questions and Answers
What does a positive Gibbs energy change (∆G°') indicate about a reaction?
What does a positive Gibbs energy change (∆G°') indicate about a reaction?
- The reaction is spontaneous.
- The reaction is exergonic.
- The reaction is at equilibrium.
- The reaction is endergonic. (correct)
Given that the equilibrium constant (Keq) is less than 1, what can be inferred about the concentrations of reactants and products at equilibrium?
Given that the equilibrium constant (Keq) is less than 1, what can be inferred about the concentrations of reactants and products at equilibrium?
- Products are favored at equilibrium.
- Reactants are favored at equilibrium. (correct)
- Both reactants and products are present in equal concentrations.
- The reaction does not proceed to equilibrium.
What happens to the reaction A ⇋ B when 1M of both A and B are mixed under standard conditions?
What happens to the reaction A ⇋ B when 1M of both A and B are mixed under standard conditions?
- The reaction proceeds to the left. (correct)
- The reaction remains static with no movement.
- The reaction proceeds to the right.
- The reaction converts completely to products.
How does the Gibbs energy change (∆G) relate to the mass-action ratio (G)?
How does the Gibbs energy change (∆G) relate to the mass-action ratio (G)?
What is the relationship between standard Gibbs energy change (∆G°) and the equilibrium constant (Keq)?
What is the relationship between standard Gibbs energy change (∆G°) and the equilibrium constant (Keq)?
What is the value of Keq at equilibrium for the reaction A ⇋ B?
What is the value of Keq at equilibrium for the reaction A ⇋ B?
Which condition results in an exergonic reaction based on the equation ∆G' = ∆Gº' + RT ln [B]/[A]?
Which condition results in an exergonic reaction based on the equation ∆G' = ∆Gº' + RT ln [B]/[A]?
What strategy is mentioned for organisms to enable reactions with positive Gibbs energy changes?
What strategy is mentioned for organisms to enable reactions with positive Gibbs energy changes?
If the [A]/[B] ratio is greater than 56.6, what can be inferred about the system?
If the [A]/[B] ratio is greater than 56.6, what can be inferred about the system?
What does the term ΔGº' represent in biochemical reactions?
What does the term ΔGº' represent in biochemical reactions?
What is the value of ∆G' when [A]/[B] = 60 at 25 °C?
What is the value of ∆G' when [A]/[B] = 60 at 25 °C?
For the reaction glucose-6-phosphate ⇋ fructose-6-phosphate, what is the value of ∆Gº'?
For the reaction glucose-6-phosphate ⇋ fructose-6-phosphate, what is the value of ∆Gº'?
At equilibrium, what is the value of ∆G' for the reaction involving glucose-6-phosphate and fructose-6-phosphate?
At equilibrium, what is the value of ∆G' for the reaction involving glucose-6-phosphate and fructose-6-phosphate?
In the context of chemical coupling, if a reaction has ∆Gº' of +10 kJ/mol, what must be true for the coupled reaction?
In the context of chemical coupling, if a reaction has ∆Gº' of +10 kJ/mol, what must be true for the coupled reaction?
What is the total change in Gibbs free energy (∆Gº') when reactions A⇋B (∆Gº' = +10 kJ/mol) and C⇋D (∆Gº' = -31 kJ/mol) are coupled?
What is the total change in Gibbs free energy (∆Gº') when reactions A⇋B (∆Gº' = +10 kJ/mol) and C⇋D (∆Gº' = -31 kJ/mol) are coupled?
Which strategy do living organisms use to allow reactions with positive Gibbs energy values to proceed spontaneously?
Which strategy do living organisms use to allow reactions with positive Gibbs energy values to proceed spontaneously?
What effect does ATP hydrolysis typically have on endergonic reactions?
What effect does ATP hydrolysis typically have on endergonic reactions?
What happens to the free energy fraction for glucose-6-phosphate (fG6P) when ∆G' is less than 0?
What happens to the free energy fraction for glucose-6-phosphate (fG6P) when ∆G' is less than 0?
What are the two strategies that living organisms use to allow reactions with positive ∆G values to occur spontaneously?
What are the two strategies that living organisms use to allow reactions with positive ∆G values to occur spontaneously?
Which of the following describes chemical coupling in the context of biochemical reactions?
Which of the following describes chemical coupling in the context of biochemical reactions?
Which example illustrates the concept of mass action effectively?
Which example illustrates the concept of mass action effectively?
In a metabolic pathway, which of the following best depicts the utilization of mass action?
In a metabolic pathway, which of the following best depicts the utilization of mass action?
What can be calculated when given the ∆G or ∆G° values for individual reactions in a metabolic pathway?
What can be calculated when given the ∆G or ∆G° values for individual reactions in a metabolic pathway?
Study Notes
Gibbs Free Energy Change (∆G)
- The Gibbs free energy change (∆G) indicates the direction and extent of a reaction’s drive towards equilibrium.
- ∆G is influenced by the equilibrium constant (Keq) and the mass-action ratio (G, the ratio of products to reactants).
- The standard Gibbs free energy change (∆Gº) directly relates to Keq.
Calculation of ∆G
- For the reaction A ⇋ B, if ∆Gº' = +10 kJ/mol, the reaction is endergonic.
- When concentrations of A and B are equal at standard conditions, the equilibrium constant (Keq) will be less than 1.
- At equilibrium, the concentration ratio [B]/[A] is approximately 0.0177.
Mass Action Effect
- To drive a reaction with a positive ∆G, maintain the mass action ratio (G) below Keq.
- Increasing substrate concentration or reducing product concentration helps achieve exergonic conditions (∆G' < 0).
Chemical Coupling
- Reactions with positive ∆G can be made spontaneous (exergonic) by coupling with a more negative ∆G reaction.
- Example: A ⇋ B (∆Gº' = +10 kJ/mol) can be coupled with C ⇋ D (∆Gº' = -31 kJ/mol) resulting in a net reaction A + C ⇋ B + D with ∆Gº' = -21 kJ/mol.
Equilibrium and Reaction Dynamics
- At equilibrium, ∆G’ equals 0, indicating no net change in reactant or product concentrations.
- When fG6P (glucose-6-phosphate) = 0.665 and fF6P (fructose-6-phosphate) = 0.335, it reflects the state at equilibrium for the conversion of glucose-6-phosphate to fructose-6-phosphate.
Living Organisms and Reactions
- Organisms utilize two main strategies to drive reactions with positive ∆G:
- Mass Action: Keeping the mass-action ratio (G) below Keq.
- Chemical Coupling: Linking reactions to those with a stronger negative ∆G.
ATP Hydrolysis as a Coupling Example
- ATP hydrolysis is often employed as a coupling mechanism to power endergonic reactions, making them exergonic.
Key Takeaway
- The integration of thermodynamic principles (mass action and chemical coupling) is critical for biological processes, allowing cells to overcome energetically unfavorable reactions and maintain metabolic pathways.
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Description
Test your understanding of thermodynamic principles in biochemistry. This quiz focuses on the calculation of Gibbs free energy changes and the mass action principle as applied to carbohydrate metabolism. Key concepts include the relationship between reactant concentrations and energy changes.
