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Volume I · MMXXVI AP Chemistry
Library› AP Chemistry› Unit 9: Thermodynamics and Electrochemistry
⁂   AP Chemistry · Unit 9

9. Thermodynamics and Electrochemistry

7–9% of the AP exam. 7 key topics. 4 common errors analyzed.

7–9% exam weight

Unit 9: Thermodynamics and Electrochemistry

Unit 9 (Thermodynamics and Electrochemistry) is part of the AP Chemistry core curriculum. Work through each key topic in sequence, constructing ICE tables, net ionic equations, or energy diagrams as appropriate.

Key topics in this unit

  1. Entropy and dispersal
  2. Gibbs free energy
  3. Thermodynamic favorability
  4. Galvanic (voltaic) cells
  5. Cell potential and standard reduction potentials
  6. Electrolysis
  7. Faraday's Law

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Justifying thermodynamic favorability using only ΔH while ignoring the ΔS contribution — full credit requires analysis of both enthalpy and entropy terms (and often their temperature dependence via ΔG = ΔH − TΔS)

Common error

Describing entropy with vague language such as 'more disorder' instead of referencing dispersal of matter or energy, number of microstates, or degrees of freedom — the College Board rubric does not award credit for the disorder analogy alone

Common error

Placing electrons on the wrong side of half-reactions in electrochemical cell problems, or confusing the sign conventions between galvanic cells (spontaneous, positive E°cell) and electrolytic cells (non-spontaneous, requires external voltage)

Common error

Applying Faraday's Law without correctly tracking moles of electrons transferred per mole of product (the stoichiometric n factor), leading to systematic errors in mass deposited or gas volume produced during electrolysis

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
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Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.