Overview
- This guide covers the 3 long free-response questions on the AP Chemistry exam
- Each long FRQ is worth 10 points (30 points total out of 50 FRQ points)
- Budget about 20-23 minutes per question (60-70 minutes total out of 105 minutes)
- These questions make up 30% of your total exam score
- Scientific or graphing calculator recommended - same formula sheet and periodic table provided
The long FRQs test your ability to work through multi-part problems that integrate several chemistry concepts. Each question typically has 6-8 parts labeled (a) through (g) or (h), with parts building on each other. You'll encounter a mix of calculations, explanations, drawings (Lewis structures, particle diagrams), and data analysis. While each question emphasizes certain units, expect to use knowledge from across the entire course.
Task verb distribution matters. The most common commands are: Calculate (perform mathematical steps with proper units), Explain (provide reasoning using chemical principles), Justify (support claims with evidence), and Draw/Represent (create diagrams or write equations). Understanding exactly what each task verb requires is key for earning full credit.
Strategic approach: These three questions vary in difficulty and style. There's typically one that's more calculation-heavy and one that's explanation-heavy. Scan all three first - takes 2 minutes but saves 10. Start with your strongest type to build confidence and momentum.
Strategy Deep Dive
Long FRQs test whether you can think through problems systematically. They're not about memorizing facts - they're about demonstrating logical problem-solving. Clear, logical work scores better than attempts at impressive vocabulary.
Reading and Planning Phase
Read the entire question first, even though it feels time-consuming. Those 2-3 minutes prevent misunderstandings that require redoing work. As you read, actively identify: What's the chemical system? What data are provided? How do the parts connect? Which formulas will you need?
This initial scan reveals the question's architecture. Part (a) might ask you to balance an equation that you'll use in part (b)'s calculation. Part (c)'s explanation might depend on the result from part (b). Part (d) might shift to a related but distinct concept. Seeing these connections prevents you from going down wrong paths or missing key relationships.
Effective marking system: circle every number value, underline key phrases like "at equilibrium" (they indicate which equations to use), and write quick formula notes in margins. This prevents having to search for crucial details later when deep in calculations.
Working Through Multi-Step Calculations
Long FRQs love multi-step calculations where each result feeds into the next. The key is maintaining accuracy while showing clear work. Start each calculation by writing what you're solving for: "Finding moles of HCl:" This helps graders follow your logic and helps you stay organized.
Units serve two crucial purposes: they earn points and verify your work. If you're calculating molarity and end up with grams, you know something went wrong. The College Board specifically instructs graders to award points for proper unit usage and significant figures, so this attention to detail directly affects your score.
When a calculation builds on a previous answer, use your calculated value even if you're unsure it's correct. The rubric often awards "consequential credit" - if your method is right, you get points even using an incorrect value from an earlier part. Never skip a calculation because you think your previous answer was wrong.
Explanation Questions
Understanding "Explain" vs "Justify" is crucial. The effective approach: state the chemistry principle, connect it to the specific problem, then conclude. Structure it like a mini-paragraph with beginning, middle, and end. Avoid circular reasoning - saying "the reaction is exothermic because it releases heat" doesn't explain anything.
Consider this approach for a typical explanation: "The entropy increases because the reaction produces 3 moles of gas from 2 moles of gas. More gas particles means more possible arrangements of the particles, which corresponds to higher entropy." Notice how this connects the observation (mole change) to the principle (entropy relates to arrangements) to reach a conclusion.
More words don't equal more points. Precise three-sentence answers often score full credit while lengthy responses miss the mark. Graders seek evidence of understanding, not volume of writing.
Rubric Breakdown
Understanding how points are awarded transforms your approach to these questions. Each long FRQ has 10 points distributed across its parts, typically:
Calculation Points (4-5 points per question)
These points reward correct mathematical work. Usually broken down as:
- 1 point for correct setup/formula selection
- 1 point for correct substitution of values
- 1 point for correct numerical answer with units
Critical scoring element: setup points exist! Even with calculation errors, writing ΔG° = ΔH° - TΔS° and correctly substituting values earns points. A clearly wrong answer like ΔG = 10,000 kJ/mol can still earn 2/3 points with correct setup.
Explanation/Justification Points (3-4 points per question)
These assess conceptual understanding:
- 1 point for identifying the relevant principle
- 1 point for correctly applying it to the scenario
- 1 point for reaching a valid conclusion
Common mistake: name-dropping concepts without connecting them. Writing "Le Chatelier's principle" earns nothing. Writing "Adding heat to this exothermic reaction shifts equilibrium left to absorb the added heat, decreasing product concentration" earns the point.
Representation Points (1-2 points per question)
Drawing Lewis structures, particle diagrams, or graphs:
- 1 point for correct electron count/particle number
- 1 point for proper structure/arrangement
For Lewis structures, this means right number of valence electrons AND reasonable geometry. For particle diagrams, correct relative numbers of each species AND appropriate representation (ions vs. molecules).
Significant Figures and Units
Significant figures consistently cost points. Writing 7.5 instead of 7.50 when given data has 3 sig figs loses a point. Circle the measurement with fewest sig figs at the start - takes 5 seconds, saves 1 point. If given 0.250 M and 25.0 mL, your answer needs 3 sig figs.
Common Long FRQ Patterns
Recognizing question types helps you anticipate what's coming and apply proven approaches.
Equilibrium-Based Questions
These often start with a reaction reaching equilibrium, then perturb the system somehow. Typical progression:
- Part (a): Write the equilibrium expression
- Part (b): Calculate K from initial data
- Part (c): Calculate concentrations at equilibrium using K
- Part (d): Explain what happens when conditions change
- Part (e): Calculate new equilibrium concentrations
Key FRQ principle: no information is extraneous. When stuck, identify unused data. The temperature mentioned in part (a) will be needed in part (e). An unusual coefficient in the balanced equation often proves crucial later.
Thermodynamics Questions
These integrate multiple thermodynamic concepts:
- Calculate ΔH° from bond energies or Hess's Law
- Determine ΔS° from states of matter or molecular complexity
- Find ΔG° and determine spontaneity
- Explain temperature dependence of spontaneity
- Connect to equilibrium constant via ΔG° = -RT ln K
Sign errors in thermodynamics are common but preventable. Remember: Breaking bonds = positive (endothermic). Forming bonds = negative (exothermic). This simple association prevents sign errors under exam pressure.
Laboratory-Based Questions
These describe an experiment and ask you to analyze results:
- Calculate theoretical yield
- Determine percent yield or percent error
- Explain sources of error (not "human error" - be specific)
- Suggest improvements to procedure
- Interpret data tables or graphs
"Human error" earns 0 points. "Some CO₂ escaped during transfer, decreasing measured mass and lowering calculated yield" earns full points. Be specific about what went wrong and how it affected results.
Acid-Base Titration Questions
Classic progression through a titration:
- Calculate initial pH
- Find pH at various points during titration
- Identify equivalence point
- Select appropriate indicator
- Explain buffer behavior
Remember the key differences: strong acid/strong base titrations have equivalence point at pH 7, weak acid/strong base above 7, strong acid/weak base below 7. This determines indicator choice.
Time Management Reality
Time allocation should match point values: Part (a) "Write the balanced equation" = 30 seconds for 1 point. Part (d) "Calculate the pH at the equivalence point" = 5 minutes for 3 points. Allocate time proportionally to maximize score.
Start by doing a quick point inventory. If part (a) is "Write the balanced equation" (usually 1 point), spend 30 seconds. If part (c) is "Calculate the pH of the resulting solution" (usually 2-3 points), allocate 3-4 minutes. This prevents you from over-investing time in low-value parts.
Work non-linearly when beneficial. If you're stuck on part (b) but part (c) says "Using your answer from part (b)..." make up a reasonable number and continue. You can circle back if time allows. Often, working through later parts gives insights that help with earlier ones.
Set a timer for 15 minutes per long FRQ. When it alerts, assess progress. If only on part (c) of 8, increase pace. This might mean condensing explanations or showing less intermediate work. A complete attempt at all parts scores better than perfect work on half the question.
Scoring reality: Feeling uncertain on some answers is normal and expected. Even top-scoring students report uncertainty on parts. The key is showing work clearly and maintaining momentum. Partial credit is substantial on long FRQs - maximize it through clear work.
Specific Techniques for Common Tasks
Drawing Lewis Structures
Lewis structure efficiency: Count electrons → Draw single bonds → Satisfy octets → Add remaining electrons as lone pairs or multiple bonds. Complete in 30 seconds. For resonance structures, identify moving electrons (usually lone pair to pi bond or vice versa). Show only the key difference, not entire redrawn structure.
Particle Diagrams
Particle diagrams must show actual species present. Strong acid: all ions, no molecules. Weak acid: mostly molecules, few ions. Match ratios to equilibrium constants - if Ka = 10⁻⁵, show approximately 1 ion pair per 100,000 molecules. For precipitation reactions: show spectator ions throughout, solid at bottom.
Graph Interpretation
First identify what's being plotted - axes labels tell the story. For titration curves, locate key features: initial pH, buffer region (gradual change), equivalence point (steep change), final pH. For kinetics plots, identify order from linearity: [A] vs time linear = zero order, ln[A] vs time linear = first order, 1/[A] vs time linear = second order.
Final Thoughts
Long FRQs distinguish top scores through systematic work and clear communication, not just content knowledge. Students who show every step and explain reasoning score higher than those with extensive memorization but poor communication.
Success comes from practice with the format, not just content knowledge. Work through released FRQs under timed conditions. Study the scoring guidelines to understand what graders actually reward. Most importantly, develop confidence in your problem-solving process.
These questions look scary but they're actually fair. Nothing requires knowledge beyond the course - they just combine topics in ways you haven't seen. Trust your prep and work through systematically. Trust your preparation, show your work clearly, and tackle each part methodically. Even partial solutions earn significant credit.
The AP Chemistry long FRQs reward systematic thinking and clear communication—cultivate these skills, and success follows. Remember that every calculation tells a chemical story, every explanation reveals molecular behavior, every diagram illustrates atomic reality. You've developed the tools to tackle these multi-layered problems. Now show that sophisticated chemical thinking.