Lecture Notes on Chemical Reactions, Gibbs Free Energy, and Enzymes

Introduction

• Understanding chemical reactions involves studying thermodynamics and kinetics.
• Key concepts include:
  • Gibbs Free Energy
  • Activation Energy
• Enzymes influence chemical reactions and their study involves these concepts.

Gibbs Free Energy (ΔG)

• Describes how much energy is available for use in a chemical reaction.
• Graphical Representation:
  • Y-axis: Energy value
  • X-axis: Reaction progress
  • ΔG = Free energy of products - Free energy of reactants
• Exergonic Reactions:
  • Negative ΔG
  • Energy is released (e.g., combustion)
  • Spontaneous reactions
• Endergonic Reactions:
  • Positive ΔG
  • Energy input required (e.g., ATP synthesis)
  • Non-spontaneous reactions
• Equilibrium:
  • ΔG = 0 indicates equilibrium
  • Rate of forward reaction equals rate of reverse reaction

Activation Energy (Eₐ)

• Energy required to initiate a reaction.
• Transition State:
  • High energy, unstable, and short-lived
  • Apex of energy diagram represents transition state
• Activation energy determines reaction speed.
  • High activation energy implies a slower reaction.
  • Spontaneity (negative ΔG) does not guarantee quick reaction.

Role of Enzymes

• Enzymes do not alter Gibbs Free Energy.
  • Energy of reactants and products remain unchanged.
  • ΔG remains the same with or without enzymes.
• Effect on Activation Energy:
  • Enzymes lower activation energy by stabilizing the transition state.
  • Lowered activation energy speeds up the reaction.
• Conclusion:
  • Enzymes speed up reactions without affecting equilibrium or ΔG.
  • They enable equilibrium to be reached faster by decreasing activation energy.