AP Chemistry Unit 9 Study Notes

AP Chemistry 9.3: Thermodynamic Favorability vs. Reaction Rate

Distinguish whether a process is favored from how quickly it occurs.

Aligned to Thermodynamics and Electrochemistry from the current College Board AP Chemistry course outline. Exam weighting for this unit: 7%-9% of the multiple-choice score range listed by College Board.

Study these notes

Start with each main idea, then follow the indented explanations and worked examples. Try the next calculation before reading its answer.

Organized from the provided Unit 9 study document. Further study: Khan Academy.

11. Favorable Does Not Mean Fast

  • This is one of the most important connections between Units 5 and 9.

  • Thermodynamics tells you whether a process is energetically favored.

  • Kinetics tells you how quickly it happens.

  • A reaction can have:

    • ΔG < 0
    • and still occur extremely slowly if it has a large activation-energy barrier.
    • Therefore:
    • thermodynamically favored ≠ fast
19. Thermodynamics vs. Kinetics

  • Keep these ideas separate.

Thermodynamics

  • Questions like:

    • Is the process favored?
    • Important quantities:
    • ΔH
    • ΔS
    • ΔG
    • K
Kinetics

  • Questions like:

    • How fast will it occur?
    • Important quantities:
    • activation energy
    • reaction mechanism
    • rate law
    • rate constant
    • A catalyst affects kinetics.
    • A catalyst does not make ΔG more negative.