electrons enter the wire
🔋AP CHEMISTRY STUDY GUIDE
Unit 9: Thermodynamics and Electrochemistry
Study entropy, Gibbs energy, thermodynamic favorability, galvanic cells, electrolysis, and cell voltage for AP Chemistry Unit 9.
8 key ideas8 flashcards5 practice questions
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Electrons leave oxidation and arrive at reduction.
electrons leave the wire
ions maintain electrical neutrality
Key ideas to know
Start with the relationships between ideas. Then close the notes and explain each one from memory.
- 01
Entropy measures the dispersal of matter and energy among available microstates.
- 02
A process can be thermodynamically favorable even when it occurs very slowly.
- 03
Gibbs energy combines enthalpy, temperature, and entropy through ΔG = ΔH − TΔS.
- 04
A negative Gibbs energy difference indicates a thermodynamically favorable forward process under stated conditions.
- 05
Standard Gibbs energy and the equilibrium constant are related through ΔG° = −RT ln K.
- 06
Oxidation occurs at the anode, while reduction occurs at the cathode.
- 07
Electrons travel through the external circuit from anode to cathode.
- 08
A positive standard cell voltage corresponds to a negative standard Gibbs energy difference for the cell reaction.
PART OF THE AP CHEMISTRY GUIDE
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Open the full AP Chemistry guide →Two ideas worth correcting now
NOT QUITE
→A favorable reaction must be fast
USE THIS INSTEAD
Thermodynamic favorability does not determine reaction rate.
NOT QUITE
→The anode is always negative
USE THIS INSTEAD
The anode is negative in a galvanic cell but positive in an electrolytic cell. Oxidation occurs there in both.
Flashcards
Answer before opening each card. The effort to retrieve is part of the learning.
1What does entropy count conceptually?Show answer ＋
The dispersal of matter and energy across accessible microstates.
2What equation connects Gibbs energy, enthalpy, temperature, and entropy?Show answer ＋
ΔG = ΔH − TΔS.
3What does a negative ΔG indicate?Show answer ＋
A thermodynamically favorable forward process under the stated conditions.
4Where does oxidation occur?Show answer ＋
At the anode.
5Where does reduction occur?Show answer ＋
At the cathode.
6Which way do electrons travel in the external circuit?Show answer ＋
From anode to cathode.
7What is the standard cell-voltage relation?Show answer ＋
E°cell = E°cathode − E°anode when tabulated reduction potentials are used.
8What does electrolysis require?Show answer ＋
External electrical energy to drive a nonfavorable redox process.
Explain it in your own words
Use the answer as a check after you have written or spoken your response.
01Why can a favorable reaction appear not to occur?
A large activation barrier can make the reaction extremely slow even when Gibbs energy favors products.
02How does increasing temperature affect a process with positive enthalpy and positive entropy differences?
The entropy term becomes more favorable at higher temperature and can make Gibbs energy negative.
03How is K related to standard Gibbs energy?
A large K corresponds to a negative standard Gibbs energy difference through ΔG° = −RT ln K.
04Why is the anode negative in a galvanic cell?
Oxidation releases electrons there, and those electrons flow through the external circuit.
05How does a salt bridge permit a galvanic cell to keep operating?
Ion movement maintains electrical neutrality in the two half-cells while electrons travel through the wire.
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