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The AP Chemistry Unit 9 Progress Check MCQ tests Thermodynamics and Electrochemistry across topics 9.1–9.11. It includes about 24 multiple-choice questions with conceptual, calculation, and stimulus-based formats. Key topics include entropy, Gibbs free energy, equilibrium relationships, galvanic vs. electrolytic cells, the Nernst equation, and Faraday’s Law. This unit is worth 7–9% of the AP Chemistry exam. Scores are auto-graded in College Board AP Classroom, and official questions are not publicly released.
The AP Chemistry Unit 9 Progress Check MCQ is an official College Board assessment on AP Classroom. Teachers assign it online, and after submission your answers are auto-scored with instant feedback and explanations.
Key Facts About the Progress Check MCQ
| Category | Details |
| Format | Approximately 24 multiple-choice questions with four choices (A, B, C, D) and one correct answer. No partial credit and no guessing penalty. |
| Access | Available through AP Classroom at myap.collegeboard.org. Assigned by your AP Chemistry teacher after enrollment. |
| Scoring | Automatically scored after submission. Students receive instant scores and explanations. Teachers can view class performance data. |
| Purpose | Formative assessment used to check mastery and identify weak areas before the AP exam. It does not directly affect your AP exam score. |
| Question Types | (1) Stand-alone conceptual questions, (2) stand-alone calculation questions, (3) stimulus-based sets using diagrams, data tables, or cell setups. |
After submission, AP Classroom usually shows your score, correct answers, and explanations for review. If your teacher locks the Progress Check, you may only see the score until review mode is unlocked. Ask your teacher to enable review access so you can study the explanations.
| Resource Type | Description | Access |
| Unit 9 Progress Check MCQ Practice Set | Practice multiple-choice questions covering thermodynamics and electrochemistry in Unit 9 format | Download |
| Unit 9 Answer Key PDF | Correct answers with step-by-step explanations for every MCQ | Download |
| Thermodynamics MCQ Practice | Questions on entropy, Gibbs free energy, spontaneity, and equilibrium | Download |
| Electrochemistry MCQ Practice | Practice on galvanic cells, electrolytic cells, cell potential, and redox reactions | Download |
| Nernst Equation Practice Sheet | Calculation questions on Q effects, concentration cells, and Ecell changes | Download |
| Faraday’s Law Practice Set | Quantitative problems on electrolysis, charge, mass deposited, and time required | Download |
| Full Unit 9 Mock Test (Timed) | Realistic timed Unit 9 test with mixed MCQs and scoring guide | Download |
| AP Chemistry Formula Sheet | One-page sheet with Unit 9 formulas, constants, and quick revision notes | Download |
| Unit 9 Common Mistakes Guide | Most common traps, sign errors, and exam tips for Progress Check MCQs | Download |
Unit 9 (Thermodynamics and Electrochemistry) includes Topics 9.1–9.11 and is worth 7–9% of the AP Chemistry test. That means about 4–6 questions on the 60-question MCQ section. Here is a complete list of the topics and the types of questions that are usually asked about each one on the Progress Check.
| Topic # | Title | What the MCQ Tests | Est. # Questions |
| 9.1 | Introduction to Entropy | Qualitative sign of DeltaS; particle disorder; comparing S for gases, liquids, solids | 2-3 |
| 9.2 | Absolute Entropy & Entropy Change | Calculating DeltaS_rxn = Sum S(products) – Sum S(reactants) using S degree tables | 1-2 |
| 9.3 | Gibbs Free Energy & Thermodynamic Favorability | DeltaG = DeltaH – TDeltaS; four sign combinations; crossover temperature | 2-3 |
| 9.4 | Thermodynamic vs. Kinetic Control | Spontaneous NOT equal to fast; thermodynamic vs. kinetic products; activation energy | 1-2 |
| 9.5 | Free Energy and Equilibrium | DeltaG degree = -RT ln K; sign of DeltaG degree determines sign of K; magnitude of K | 2-3 |
| 9.6 | Coupled Reactions | DeltaG_overall = DeltaG_1 + DeltaG_2; K_overall = K_1 x K_2; driving nonspontaneous reactions | 1-2 |
| 9.7 | Galvanic & Electrolytic Cells: Similarities | Anode = oxidation; cathode = reduction; electron flow; ion migration in salt bridge | 2-3 |
| 9.8 | Galvanic & Electrolytic Cells: Differences | Spontaneous vs. nonspontaneous; E_cell sign; anode/cathode charge conventions differ | 2-3 |
| 9.9 | Cell Potential Under Nonstandard Conditions | Nernst equation; effect of Q on E_cell; concentration cells; Q vs. K comparison | 2-3 |
| 9.1 | Cell Potential, Free Energy & Equilibrium | DeltaG degree = -nFE degree; sign triangle (E, DeltaG, K); magnitude relationships | 1-2 |
| 9.11 | Electrolysis & Faraday’s Law | Q = It; mol e- = Q/F; stoichiometric ratio; mass deposited; time required | 2-3 |
The most tested Unit 9 topics are: Gibbs free energy and spontaneity (9.3/9.5), galvanic vs. electrolytic cells (9.7/9.8), the Nernst equation (9.9), and Faraday’s Law calculations (9.11). These areas make up about 60–70% of Unit 9 MCQs, so master them first.
The Three Question Formats on the Unit 9 Progress Check MCQ
| Format | What It Looks Like | AP Chemistry Example | Approx. Count |
| Stand-alone conceptual | One question; one concept; no calculation required. Tests pure understanding of a principle. | Which of the following reactions has DeltaS > 0?’ with four balanced equations | ~8-10 |
| Stand-alone quantitative | One question requiring a multi-step calculation. Tests formula application and algebraic manipulation. | A current of 3.00 A is applied for 1,000 s. What mass of Cu is deposited?’ | ~6-8 |
| Stimulus-based set | A shared figure, table, or data set followed by 3-4 related questions. Requires reading the stimulus accurately before answering. | A table of standard reduction potentials followed by 4 questions on E_cell, spontaneity, Nernst, and DeltaG | ~8-10 |
Every wrong answer on a Unit 9 Progress Check MCQ is engineered to match a specific error. Knowing these traps is as valuable as knowing the correct answers:
| Trap Name | The Error | The Fix |
| The Positive-is-Spontaneous Trap | Student marks DeltaG > 0 as spontaneous (backward convention). Correct: DeltaG < 0 is spontaneous. | Memorize: favorable = negative DeltaG. Unfavorable = positive DeltaG. Always. |
| The Celsius-Not-Kelvin Trap | Student uses T = 720 instead of T = 993 K in DeltaG = -RT ln K or Nernst equation. | First step on any thermos or electrochemistry calculation: convert T to Kelvin (add 273). |
| The Q-Increases-E_cell Trap | Student believes more products (Q > 1) means more cell driving force. Backward. | Q > 1 means products accumulate -> ln Q is positive -> subtracted from E_degree -> E_cell DECREASES. |
| The Anode-Is-Positive-Always Trap | Student applies galvanic anode convention (negative) to electrolytic cell. Wrong. | Anode = oxidation ALWAYS. But anode charge sign differs: galvanic anode = negative; electrolytic anode = positive. |
| The Divide-By-n Trap in Faraday | Student computes mol e- but forgets to divide by n from the half-reaction. | Write the half-reaction first. Count electrons explicitly. mol substance = mol e- / n. |
Entropy questions test both qualitative prediction (sign of DeltaS) and quantitative calculation (value of DeltaS_rxn). The most important skill: predicting DeltaS from the moles of gas, not from intuition about complexity.
The Rules the MCQ Tests Every Year
| Concept | Key Rule |
| ΔS > 0 (Entropy Increases) | Gas moles increase, solids/liquids dissolve into ions, phase changes toward gas, more particles formed. |
| ΔS < 0 (Entropy Decreases) | Gas moles decrease, ions form solids, gas condenses to liquid, fewer particles formed. |
| Standard Molar Entropy (S°) | Always positive. Increases with molar mass, phase (gas > liquid > solid), and molecular complexity. |
| Calculating ΔS_rxn | ΔS_rxn = Σ(n × S°products) − Σ(n × S°reactants) using stoichiometric coefficients. |
CaCO₃(s) → CaO(s) + CO₂(g)
What is the sign of ΔS°?
a. ΔS° < 0, solid breaks apart
b. ΔS° < 0, solids decrease
c. ΔS° > 0, gas is produced
d. ΔS° > 0, CO₂ has higher molar mass
Producing CO₂(g) from solid reactants increases disorder because gases have much greater freedom of motion. Therefore ΔS° > 0.
Gibbs free energy is one of the toughest and most tested Unit 9 topics. You must solve ΔG = ΔH – TΔS, relate ΔG° to K, and analyze coupled reactions. These questions cause many of the most common MCQ mistakes.
The Four DeltaH/DeltaS Sign Combinations – Memorize the Entire Table
| Delta H | Delta S | Delta G = Delta H – Delta S | Spontaneous? | Temperature Dependence |
| Negative (exo) | Positive (disorder increases) | Always negative | Always – at any temperature | None -always spontaneous |
| Negative (exo) | Negative (disorder decreases) | Negative at low T; positive at high T | Only at LOW temperatures | Spontaneous only below T = DeltaH/DeltaS |
| Positive (endo) | Positive (disorder increases) | Positive at low T; negative at high T | Only at HIGH temperatures | Spontaneous only above T = DeltaH/DeltaS |
| Positive (endo) | Negative (disorder decreases) | Always positive | Never – at any temperature | None – never spontaneous |
For a reaction: ΔH° = +55 kJ/mol, ΔS° = +110 J/mol·K
When is the reaction favorable?
a. Favorable at all temperatures
b. Only below 500 K
c. Only above 500 K
d. Never favorable
Use ΔG = ΔH – TΔS. Convert units: 55 kJ = 55,000 J.
Crossover temperature:
T = ΔH / ΔS = 55,000 / 110 = 500 K
Above 500 K, ΔG < 0, so the reaction is spontaneous.
| Delta G degree Value | K value | Interpretation | E degree_cell |
| DeltaG degree < 0 (negative) | K > 1 | Products favored at equilibrium -thermodynamically favorable as written | E degree > 0 (positive) |
| DeltaG degree = 0 | K = 1 | Neither products nor reactants favored – equilibrium at standard conditions | E degree = 0 |
| DeltaG degree > 0 (positive) | K < 1 | Reactants favored at equilibrium – NOT thermodynamically favorable as written | E degree < 0 (negative) |
Cell analysis questions are common on the Unit 9 Progress Check MCQ. You must identify the anode, cathode, electron flow, and tell the difference between galvanic and electrolytic cells. These often appear with cell diagrams or standard reduction potential tables.
Complete Galvanic vs. Electrolytic Cell Comparison
| Feature | Galvanic (Voltaic) Cell | Electrolytic Cell |
| Energy conversion | Chemical energy to electrical energy | Electrical energy to chemical energy |
| Reaction type | Spontaneous (DeltaG < 0) | Nonspontaneous (DeltaG > 0); requires external power supply |
| E degree_cell sign | Positive (E degree > 0) | Negative (E degree < 0) – must apply external voltage to drive |
| Anode reaction | Oxidation (mass decreases – metal dissolves) | Oxidation (same reaction type as galvanic) |
| Anode terminal charge | NEGATIVE (electrons leave, travel through external circuit) | POSITIVE (connected to + terminal of power supply) |
| Cathode reaction | Reduction (mass increases – metal deposits) | Reduction (same reaction type as galvanic) |
| Cathode terminal charge | POSITIVE | NEGATIVE (connected to – terminal of power supply) |
| Electron flow direction | Anode to cathode through external wire | From external power source – into cathode; from anode back to source |
| Ion migration in salt bridge | Cations toward cathode; anions toward anode (same for both cell types) | Cations toward cathode; anions toward anode (same rule) |
| Real-world examples | Batteries, fuel cells, lemon/potato clock | Electroplating, electrolysis of water, aluminum refining, charging a dead battery |
AP Chemistry is easier to learn when you have the correct Study Resources. To help students improve their comprehension and test performance, TestprepKart provides a number of free downloadable e-books that cover every essential idea and formula required to succeed in AP Chemistry and other AP science courses.
The Nernst equation is one of the most tested Unit 9 calculation topics and a common source of sign errors. Master the formula, how Q affects Ecell, and how concentration cells operate.
Full form: E_cell = E degree_cell – (RT/nF) ln Q
At 25 C (298 K) simplified: E_cell = E degree_cell – (0.0592/n) log Q
| Variable | What It Means | Common Source of Error |
| E_cell | Actual cell potential under the given (nonstandard) conditions | Do not confuse with E degree_cell – that is the standard-state value |
| E degree_cell | Standard cell potential: all concentrations 1 M, all gas pressures 1 atm, 25 C | Calculate using E degree_cell = E degree_cathode – E degree_anode from a reduction potential table |
| R | Gas constant = 8.314 J/mol-K | Must use R = 8.314, not 0.08206 (that is in L-atm for ideal gas law) |
| T | Temperature in Kelvin ONLY | Students use Celsius – always convert first: K = Celsius + 273 |
| n | Moles of electrons transferred in the balanced redox equation | Come from the balanced half-reactions, not assumed to be 1 |
| F | Faraday’s constant = 96,485 C/mol e- | This appears in both the Nernst equation and Faraday’s law calculations |
| Q | Reaction quotient: [products]/[reactants] (pure solids and liquids excluded) | Must exclude pure solids/liquids; include only aqueous and gas species |
Cell Potential & Gibbs Free Energy MCQ Answers (Topic 9.10)
The relationship between E degree_cell, DeltaG degree, and K is the conceptual core of electrochemistry in Unit 9. A single question can test all three simultaneously — and they always point in the same direction.
| E degree_cell | DeltaG degree | K | Spontaneous? | Cell Type |
| E degree > 0 (positive) | DeltaG degree < 0 (negative) | K > 1 | YES | Galvanic -produces electricity spontaneously |
| E degree = 0 | DeltaG degree = 0 | K = 1 | At equilibrium | No net flow; system at equilibrium under standard conditions |
| E degree < 0 (negative) | DeltaG degree > 0 (positive) | K < 1 | NO | Electrolytic – requires external electrical energy to drive |
Faraday’s Law quantitative problems are among the most predictable on the entire AP Chemistry exam. The four-step chain is always the same. If you can execute it without procedural errors, you earn these points every time.
| Step | What to Do | Formula |
| Step 1 | Convert current and time to coulombs | Q = I × t |
| Step 2 | Convert coulombs to moles of electrons | mol e⁻ = Q / 96,485 |
| Step 3 | Convert electrons to moles of substance | Use half-reaction ratio |
| Step 4 | Convert moles to mass | mass = mol × molar mass |
These practice questions span all major Unit 9 topic areas in authentic AP Chemistry Progress Check MCQ format. Work through all timed (15 minutes total – 1.5 minutes per question), then review the explanations for every question whether you got it right or wrong.
Practice 1 — Entropy (Topic 9.1)
Two samples of the same substance are at the same temperature:
A = Gas, B = Liquid. Which is correct?
a. S°(A) = S°(B)
b. S°(A) > S°(B)
c. S°(B) > S°(A)
d. Equal only for monatomic elements
Entropy increases by phase: solid < liquid < gas. Gas particles have more freedom of motion and more accessible microstates, so S°(gas) > S°(liquid).
Practice 2 — Gibbs Free Energy (Topic 9.3)
At 25°C, a reaction has ΔH° = -120 kJ/mol and ΔS° = -200 J/mol·K. What happens at 800 K?
a. Favorable because ΔH is negative
b. Favorable because ΔS is negative
c. Not favorable because TΔS makes ΔG positive
d. Never favorable when both are negative
Use ΔG = ΔH – TΔS.
At high temperature, the TΔS term becomes important.
ΔG = -120,000 – (800 × -200) = +40,000 J/mol
Since ΔG > 0, the reaction is not favorable at 800 K.
Based on College Board reports and scoring trends, these Unit 9 MCQ patterns cause the most mistakes. Review them before your Progress Check to avoid common errors and gain easy points.
| Missed Concept | What Students Do Wrong | What the Correct Reasoning Is | Frequency |
| Predicting DeltaS sign | Counting atoms or molecular complexity instead of moles of gas | Count ONLY the change in moles of GAS between reactants and products. More mol gas = DeltaS > 0. Fewer mol gas = DeltaS < 0. | Very High |
| Celsius in thermo calculations | Plugging T in Celsius into DeltaG = -RT ln K or Nernst | Convert FIRST: K = Celsius + 273. The formulas are derived in Kelvin and fail completely with Celsius. | Very High |
| Positive DeltaG = spontaneous | Reversing the DeltaG sign convention | Negative DeltaG = spontaneous = thermodynamically favorable. Positive DeltaG = nonspontaneous. | High |
| Q > 1 increases E_cell | Thinking more products means more reaction driving force | Q > 1 means products have accumulated. Nernst: E_cell = E degree – (0.0592/n) log Q. Larger Q -> larger subtraction -> LOWER E_cell. | High |
| Electrolytic anode is negative | Applying galvanic anode convention to electrolytic cell | Galvanic: anode = negative. Electrolytic: anode = POSITIVE (connected to + of power supply). The reaction (oxidation) is the same; the charge is different. | High |
| Forgetting n in Faraday’s law | Computing mol e- but reporting it as mol of substance | ALWAYS divide mol e- by n from the half-reaction. If n = 2 (Cu2+ + 2e- -> Cu), then mol Cu = mol e- / 2. | High |
| Coupled reaction: adding K values | Adding K1 + K2 instead of multiplying | DeltaG is additive: DeltaG_total = DeltaG1 + DeltaG2. K multiplies: K_total = K1 x K2. These are DIFFERENT operations for the same two reactions. | Medium |
The AP Chemistry exam provides a formula and constants sheet on exam day. You must know when to apply each formula and what each variable represents. Every formula below appears on at least one Unit 9 Progress Check MCQ.
| Formula | Variables and Units | When to Apply on the MCQ |
| DeltaS degree_rxn = Sum(n x S degree_products) – Sum(n x S degree_reactants) | S degree in J/mol-K; n = stoichiometric coefficients | When given a table of S degree values and asked to calculate DeltaS degree for a reaction |
| DeltaG degree = DeltaH degree – T x DeltaS degree | T in Kelvin; Delta H in J (not kJ) if Delta S is in J/mol-K | Calculating DeltaG degree; predicting spontaneity; finding crossover temperature T = DeltaH/DeltaS |
| DeltaG degree = -RT ln K | R = 8.314 J/mol-K; T in Kelvin | Connecting DeltaG to K; finding K from DeltaG or DeltaG from K |
| DeltaG = DeltaG degree + RT ln Q | Q = reaction quotient under actual conditions | DeltaG under non-standard conditions; at equilibrium DeltaG = 0 and Q = K |
| DeltaG degree_overall = DeltaG degree_1 + DeltaG degree_2 | Algebraic addition | Coupled reactions – adding individual DeltaG values |
| K_overall = K_1 x K_2 | Multiply (never add) equilibrium constants | Coupled reactions – finding overall K from individual K values |
| Formula | Variables and Units | When to Apply on the MCQ |
| E degree_cell = E degree_cathode – E degree_anode | Both are standard reduction potentials from table; subtract, do not flip signs | Calculating standard cell potential from a reduction potential table |
| DeltaG degree = -nFE degree_cell | n = mol e- transferred; F = 96,485 C/mol | Connecting cell potential to Gibbs free energy; verifying spontaneity |
| E_cell = E degree_cell – (RT/nF) ln Q | At 25 C: E_cell = E degree – (0.0592/n) log Q | Cell potential under nonstandard conditions — Nernst equation |
| Q (for cell reaction) | [products]/[reactants]; exclude pure solids and pure liquids | Calculating Q to insert into Nernst equation |
| Q = I x t | I = current in Amperes; t = time in SECONDS | Charge in Coulombs for electrolysis; first step in any Faraday’s law problem |
| mol e- = Q / F | F = 96,485 C/mol e- | Convert Coulombs to moles of electrons |
| mol substance = mol e- / n | n = electrons per formula unit from half-reaction | Convert moles of electrons to moles of substance; critical step students skip |
| mass (g) = mol x molar mass | Molar mass from periodic table in g/mol | Final step in Faraday’s law: convert moles to grams |
Unit 9 MCQs are written to test specific misconceptions. Every wrong answer choice is a deliberate distractor. Knowing the distractor patterns lets you eliminate wrong answers even under time pressure
| Trap | Common Mistake | Correct Check |
| Sign Flip | Correct magnitude but wrong sign for ΔG° | Verify with ΔG° = -RT ln K or ΔG° = -nFE°cell |
| Celsius Trap | Using °C instead of Kelvin | Convert first: K = °C + 273 |
| n Error | Forgetting to divide by electrons transferred | Use mol substance = mol e⁻ / n |
| Backward Q Effect | Assuming Q > 1 increases Ecell | In Nernst equation, Q > 1 lowers Ecell |
| Question Type | Target Time | Best Strategy |
| Conceptual Sign Questions | 45–60 sec | Use memorized rules for ΔS sign, ΔG sign, cell type |
| Standard Cell Potential | 60–90 sec | Identify cathode (higher E°), then subtract |
| ΔG from K or K from ΔG | 60–90 sec | Write formula, substitute values, solve |
| Nernst Equation | 90–120 sec | Write formula, find n and Q, calculate |
| Faraday’s Law | 120–150 sec | Use the four-step conversion chain before math |
| Stimulus-Based Sets | 60 sec reading + 60 sec each question | Read stimulus once, then answer without re-reading |
Q: How do I calculate E°cell from standard reduction potentials?
Use E°cell = E°cathode − E°anode. The half-reaction with the more positive reduction potential is the cathode, and the less positive value is the anode. Use the values directly from the table and subtract—do not manually flip signs.
Q: What is the most common mistake on the AP Chemistry Unit 9 MCQ?
The biggest mistakes are using Celsius instead of Kelvin, confusing the sign of ΔG° and spontaneity, and forgetting to divide by n in Faraday’s Law calculations.
Q: What is the difference between galvanic and electrolytic cells?
Galvanic cells are spontaneous (ΔG < 0, E° > 0) and convert chemical energy into electrical energy. Electrolytic cells are nonspontaneous (ΔG > 0, E° < 0) and require external electricity. In both types, anode = oxidation and cathode = reduction.
Q: How does the Nernst equation affect cell potential on the Progress Check MCQ?
The Nernst equation is Ecell = E°cell − (0.0592/n) log Q at 25°C. Q is the reaction quotient using products over reactants, excluding pure solids and liquids.
A common MCQ mistake is thinking Q > 1 increases cell potential—it actually lowers it.
This guide is based on official College Board sources, including the AP Chemistry CED (2025 – 26), AP Classroom format, and past exam data. It is written by experienced AP Chemistry educators with 10+ years of teaching and exam coaching.
All concepts, formulas, and MCQs are aligned with current Unit 9 standards and verified using official guidelines. The content is original, exam-focused, and designed to help students understand – not memorize. No paid content or proprietary questions are included.
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