Thermodynamics and Electrochemistry Exam Notes

9.1 Introduction to Entropy

• Definition of Entropy: Measures the disorder in a system.

  • Entropy increases with temperature due to greater particle movement.

  • Physical state changes (solid to liquid to gas) significantly increase entropy.

Factors Affecting Entropy

• Temperature Increases: Leads to higher kinetic energies and more disorder.

• State Changes:

  • Solid → Liquid: Increased mobility leads to entropy increase.

  • Liquid → Gas: Significant rise in disorder due to particle separation.

• Mixtures vs. Pure Substances: Mixtures exhibit higher entropy than pure substances due to increased disorder in combinations of different molecules.

9.2 Absolute Entropy and Entropy Change

• Third Law of Thermodynamics states that a perfect crystal at absolute zero (0 K) has zero entropy.

Example Calculation

• Given:

  • Product Entropy Contributions: 192 J/(mol·K), 4*(70 J/(mol·K)), and 81 J/(mol·K)

  • Reactant Contributions: 336 J/(mol·K)

  • Calculation yields: 217 J/(mol·K) increase.

9.3 Gibbs Free Energy and Thermodynamic Favorability

• Gibbs Free Energy (G): Determines if a reaction is thermodynamically favorable.

  • Relation to Entropy: \Delta G = \Delta H - T\Delta S

  • Negative ΔG indicates a thermodynamically favorable reaction.

• Role of Temperature: Influences whether a reaction is driven by enthalpy (ΔH) or entropy (ΔS).

9.4 Thermodynamic and Kinetic Control

• Difference Between Thermodynamics and Kinetics: Thermodynamics reveals if a reaction is favorable; kinetics explains the speed and pathway of the reaction.

• Consideration of Activation Energy: Important for understanding reaction rates; thermodynamics does not account for this.

9.5 Free Energy and Equilibrium

• Relation of Gibbs Free Energy to Equilibrium: Only one reaction direction can be favored under a specific set of conditions.

  • Influence of reaction quotient (Q) on Gibbs free energy and the system's state.

9.6 Free Energy of Dissolution

• Driving Forces: Enthalpy and entropy both influence solubility.

  • The process is often driven by an increase in entropy upon dissolving.

9.7 Coupled Reactions

• Driving Non-favored Reactions: Non-favored reactions can proceed by coupling with favored reactions (e.g., in electrochemical processes).

9.8 Galvanic (Voltaic) and Electrolytic Cells

• Functions and Reactions: Galvanic cells convert chemical energy into electrical energy; electrolytic cells require an external source of electricity.

• Oxidation and Reduction Designations: Clarification of electrode processes in galvanic and electrolytic cells.

9.9 Cell Potential and Free Energy

• Nernst Equation Relating E° to ΔG°:

  • \Delta G = -nFE

• Calculated Cell Potential: Determined using standard reduction potentials and Faraday's constant.

9.10 Cell Potential Under Non-standard Conditions

• Understanding Reaction Dynamics: Influence of concentration changes on reaction viability and cell potential.

9.11 Electrolysis and Faraday’s Law

• Proportionality in Electrolysis: Mass of product at electrodes is proportional to the amount of electricity passed.

• Current Calculation: Understand charge transfer in electrolysis to deduce quantities and practical applications in various reactions.