AP Chemistry Unit 9 practice questions: Thermodynamics and Electrochemistry
8 original multiple-choice questions on AP Chem Unit 9, thermodynamics and electrochemistry. Answer each one in your browser and read the explanation, then review the key ideas below.
Question 1 of 8
A reaction has ΔH < 0 and ΔS > 0. When is it thermodynamically favorable?
Question 2 of 8
In a galvanic (voltaic) cell, where does oxidation occur?
Question 3 of 8
A cell has a positive standard cell potential, E°cell > 0. What does this mean about ΔG°?
Question 4 of 8
A reaction has K > 1 at 25 °C. What is the sign of ΔG°?
Question 5 of 8
A current of 2.0 A runs for 965 s. How many moles of electrons pass through the circuit? (F = 96,500 C/mol)
Question 6 of 8
Which process has the largest increase in entropy?
Question 7 of 8
E° for Zn²⁺/Zn is −0.76 V and for Cu²⁺/Cu is +0.34 V. What is E°cell for a zinc-copper galvanic cell?
Question 8 of 8
What is the sign of ΔS for 2H₂(g) + O₂(g) → 2H₂O(g)?
Key ideas in Unit 9
- Entropy (S) measures dispersal of matter and energy; gases have far more entropy than liquids or solids.
- Gibbs free energy: ΔG = ΔH − TΔS. A process is thermodynamically favorable when ΔG < 0.
- ΔG° = −RT ln K, so K > 1 when ΔG° is negative.
- In galvanic cells, oxidation happens at the anode and reduction at the cathode; E°cell = E°cathode − E°anode, and ΔG° = −nFE°.
- Electrolysis uses electrical energy to drive unfavorable reactions; moles of electrons = charge ÷ 96,485 C/mol.
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