Study Notes
Gibbs free energy change (ΔG) helps determine the feasibility of a chemical reaction by considering both enthalpy and entropy changes. It is calculated using the Gibbs equation: ΔG = ΔH - TΔS.
- Gibbs Free Energy (G) — the energy change that accounts for both enthalpy and entropy changes in a reaction. Example: ΔG = ΔH - TΔS, where ΔG is Gibbs free energy change, ΔH is enthalpy change, and TΔS is the temperature multiplied by entropy change.
- Standard Gibbs Free Energy Change (ΔG°) — calculated from the standard free energies of formation. Example: ΔG° can be determined using standard free energies of formation for reactants and products.
- Reaction Feasibility — determined by the sign of ΔG. Example: If ΔG < 0, the reaction is spontaneous; if ΔG > 0, it is nonspontaneous; if ΔG = 0, the reaction is at equilibrium.
Exam Tips
Key Definitions to Remember
- Gibbs Free Energy (G)
- Standard Gibbs Free Energy Change (ΔG°)
- Reaction Feasibility
Common Confusions
- Confusing the signs of ΔG with reaction spontaneity
- Misunderstanding the effect of temperature on ΔG
Typical Exam Questions
- What does a negative ΔG indicate about a reaction? A negative ΔG indicates that the reaction is spontaneous.
- How can you calculate ΔG° using standard free energies of formation? By using the formula ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants).
- How does temperature affect the feasibility of a reaction? Temperature affects feasibility depending on the signs and magnitudes of ΔH and ΔS.
What Examiners Usually Test
- Ability to calculate ΔG using the Gibbs equation
- Understanding of how temperature influences reaction feasibility
- Interpretation of ΔG values in terms of reaction spontaneity