Lecture 9 : 𝐁𝐢𝐨𝐜𝐡𝐞𝐦𝐢𝐬𝐭𝐫𝐲 - Standard Free Energy & Equilibrium

Introduction

This tutorial covers the key concepts of Standard Free Energy and Equilibrium as presented in Lecture 9 of the Biochemistry series. Understanding these concepts is crucial for grasping fundamental biochemical processes and their thermodynamic principles, which are vital for fields like biochemistry and molecular biology.

Step 1: Understanding Reaction Spontaneity

• Definition of ΔG: The change in Gibbs free energy (ΔG) indicates the spontaneity of a reaction.
• Signs of ΔG:
  • ΔG < 0: The reaction is spontaneous.
  • ΔG > 0: The reaction is non-spontaneous.
• Relation with ΔH and ΔS:
  • ΔG is influenced by both enthalpy (ΔH) and entropy (ΔS) changes:
    • Depending on the signs of ΔH (enthalpy change) and ΔS (entropy change), the spontaneity of a reaction can vary.
    • Example:
      • If ΔH is negative and ΔS is positive, ΔG is always negative (spontaneous).
      • If ΔH is positive and ΔS is negative, ΔG is always positive (non-spontaneous).

Step 2: Analyzing Forward and Backward Reactions

• ΔG of Reactions:
  • The ΔG of the forward reaction can be calculated and compared with the reverse reaction.
  • If ΔG of the forward reaction is negative, the reverse reaction will have a positive ΔG.

Step 3: Exploring the Third Law of Thermodynamics

• Concept Overview:
  • The third law states that as the temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.
  • Understanding this law is crucial for interpreting thermodynamic principles in biochemical reactions.

Step 4: Introduction to Gibbs Free Energy

• Gibbs Free Energy Equation:
  • The equation is defined as:

    ΔG = ΔH - TΔS
    

  • Where:
    • ΔG = Gibbs free energy change
    • ΔH = change in enthalpy
    • T = temperature in Kelvin
    • ΔS = change in entropy
• Practical Tip: Use this equation to assess whether a reaction will occur under specific conditions.

Step 5: Understanding Chemical Equilibrium

• Equilibrium Concept:
  • A state where the rates of the forward and backward reactions are equal, resulting in constant concentrations of reactants and products.
• Le Chatelier's Principle:
  • If an external change is applied to a system at equilibrium, the system adjusts to counteract that change and restore equilibrium.

Step 6: Calculating Equilibrium Constant (Keq)

• Keq Formula:
  • The equilibrium constant can be expressed as:

    Keq = [Products] / [Reactants]
    

  • Where square brackets denote concentrations at equilibrium.
• Application:
  • This constant helps predict the direction of the reaction and the concentrations of reactants and products at equilibrium.

Step 7: Relating Keq and ΔG°

• Connection:
  • The relationship between the equilibrium constant and standard free energy change (ΔG°) is given by:

    ΔG° = -RT ln(Keq)
    

  • Where:
    • R = gas constant
    • T = temperature in Kelvin
• Practical Implication: This equation allows researchers to understand the thermodynamics of biochemical reactions.

Conclusion

This tutorial provided an overview of critical concepts in biochemistry regarding Standard Free Energy and Equilibrium. Key takeaways include the importance of ΔG in predicting reaction spontaneity, the equilibrium concepts governing biochemical processes, and the relationships between ΔG, Keq, and thermodynamic principles. Further study on these topics will deepen your understanding of biochemical reactions and their applications in life sciences.