AP Chemistry Last-Minute Review (Night Before)

title: "AP Chemistry Last-Minute Review (Night Before)" description: "The night-before AP Chemistry checklist: essential formulas, IMF ranking, periodic trends, ICE table rules, common traps, and morning-of advice. Skim in 45 minutes." date: "2026-01-15" examDate: "May AP Exam" topics:

• Formula Sheet
• Common Traps
• Quick Reference

The exam is tomorrow. This is not the time to learn new content — it's the time to skim, reset, and sleep. Spend 30-45 minutes on this page, then put your notes away.

Essential formulas (on your exam sheet OR memorize now)

| Concept | Formula | |---|---| | pH | $pH = -\log [H^+]$ | | pOH | $pOH = -\log [OH^-]$ | | Relationship | $pH + pOH = 14$ | | Weak acid $K_a$ | $K_a = \frac{[H^+][A^-]}{[HA]}$ | | Weak base $K_b$ | $K_b = \frac{[OH^-][B]}{[BH^+]}$ | | Henderson-Hasselbalch | $pH = pK_a + \log \frac{[A^-]}{[HA]}$ | | Gibbs free energy | $\Delta G = \Delta H - T\Delta S$ | | Link to $K$ | $\Delta G = -RT \ln K$ | | Equilibrium constant | $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ (for $aA + bB \rightleftharpoons cC + dD$) | | Gas constant | $R = 8.314$ J/(mol·K) = 0.0821 L·atm/(mol·K) | | Faraday constant | $F = 96,485$ C/mol | | Ideal Gas Law | $PV = nRT$ | | Calorimetry | $q = mc\Delta T$ | | Cell potential | $E = E° - \frac{0.0592}{n}\log Q$ (Nernst) | | Electron configuration | Fill in order: 1$s$, 2$s$, 2$p$, 3$s$, 3$p$, 4$s$, 3$d$, 4$p$ ... |

Periodic trends (from left to right, top to bottom)

| Trend | Direction | Example | |---|---|---| | Atomic radius | Decreases | Na > Mg > Al > Si | | Ionization energy | Increases | Na < Mg < Al < Si | | Electron affinity | Increases (becomes more negative) | F has highest | | Electronegativity | Increases | H: 2.1, C: 2.5, N: 3.0, O: 3.4, F: 4.0 |

IMF ranking (strongest to weakest)

1. Ionic bonds (not really an IMF, but strongest inter-particle force)
2. Hydrogen bonds (N-H···O, O-H···N, F-H···F, O-H···O)
3. Dipole-dipole (polar molecules without hydrogen bonding)
4. London dispersion (nonpolar molecules; increases with surface area + molar mass)

Ranking boiling points: Ionic compounds > hydrogen-bonded > dipolar > nonpolar. Example: NaCl (1411°C) > H₂O (100°C) > HCl (-85°C) > Cl₂ (-35°C).

Top 12 traps that cost real points on exam day

1. Forgetting that solids and pure liquids are NOT included in $K_c$ or $K_p$ expressions. Example: For $CaCO_3(s) \rightleftharpoons Ca^{2+}(aq) + CO_3^{2-}(aq)$, $K = [Ca^{2+}][CO_3^{2-}]$ (no denominator).

2. Using moles instead of molarity in ICE tables for $K_c$ calculations. $K_c$ requires molarity (M), not moles.

3. Forgetting the coefficient in front of the variable in ICE tables. For $2NO_2 \rightleftharpoons N_2O_4$, the change for NO₂ is $-2x$, not $-x$.

4. Confusing $K_c$ and $K_p$ conversion. Remember: $K_p = K_c(RT)^{\Delta n}$ where $\Delta n$ = (moles of gas products) - (moles of gas reactants).

5. In a buffer, forgetting that strong acid/base problems require an ICE table. If 0.010 mol $HCl$ is added to a buffer, first do an ICE table to see how much $H^+$ and $A^-$ remain, then use Henderson-Hasselbalch.

6. Mixing up equivalence point (where moles acid = moles base) with half-equivalence point (where $pH = pK_a$). Half-equivalence is where buffer capacity is maximum.

7. Writing $\Delta G = \Delta H - T\Delta S$ but forgetting temperature must be in Kelvin. Example: At 25°C = 298 K, not 25 K.

8. On initial-rate experiments, using direct substitution instead of the ratio method. Always use $\frac{\text{Rate}_1}{\text{Rate}_2} = \left(\frac{[A]_1}{[A]_2}\right)^{\text{order}}$ to find the order.

9. Forgetting to round significant figures at the end of multi-step problems. Don't round intermediate answers.

10. On redox reactions, forgetting to balance charge as well as atoms in acidic/basic solution. Add $H^+$ in acidic, $OH^-$ in basic, and $H_2O$ to balance oxygen.

11. Assuming a reaction is spontaneous just because $\Delta H < 0$ (negative). You must check $\Delta G = \Delta H - T\Delta S$. A reaction with large positive $\Delta S$ can be spontaneous even if $\Delta H > 0$.

12. Confusing Le Chatelier prediction when pressure changes. Pressure shifts equilibrium only if there's a change in moles of gas. A reaction with equal moles of gas on each side (e.g., $H_2 + I_2 \rightleftharpoons 2HI$) is not shifted by pressure change.

Quick reference: when to use what formula

| Scenario | Formula/Approach | |---|---| | Given $K_a$, need pH of weak acid | $K_a = \frac{[H^+]^2}{C - [H^+]}$ or approx. $[H^+] = \sqrt{K_a \cdot C}$ | | Buffer pH question | Henderson-Hasselbalch: $pH = pK_a + \log \frac{[A^-]}{[HA]}$ | | Need $\Delta G$ from $K$ | $\Delta G = -RT \ln K$ | | Need $\Delta H$ from reaction data | Hess's Law or $\Delta H_{\text{rxn}} = \sum \Delta H_{\text{products}} - \sum \Delta H_{\text{reactants}}$ | | Rate law from initial rates | Ratio method: $\frac{\text{Rate}_1}{\text{Rate}_2} = \left(\frac{[A]_1}{[A]_2}\right)^{\text{order}}$ | | Spontaneity at non-standard $T$ | $\Delta G = \Delta H - T\Delta S$ (check sign at your temperature) | | Gas-phase equilibrium | Convert $K_c$ to $K_p$ using $K_p = K_c(RT)^{\Delta n}$ |

Formula sheet recall (what you'll have, what you won't)

You WILL have:

• $pH = -\log [H^+]$, $K_a = \frac{[H^+][A^-]}{[HA]}$, $pH = pK_a + \log \frac{[A^-]}{[HA]}$
• $\Delta G = \Delta H - T\Delta S$, $\Delta G = -RT \ln K$
• $E = E° - \frac{0.0592}{n}\log Q$ (Nernst)
• Gas constant $R$ and $F$ (Faraday)
• Common $K_a$ values for weak acids
• Standard reduction potentials

You will NOT have but should memorize:

• $K_a \cdot K_b = K_w$ (always true for conjugate pairs)
• How to write Lewis structures (this is a process, not a formula)
• Rules for assigning oxidation states
• How to balance redox reactions in acidic/basic solution

Score boundaries (recent years)

Out of 60 multiple-choice + 60 free-response (total 120 points):

• 5: ~70+% (≈84+ points)
• 4: ~60-69%** (≈72-83 points)
• 3: ~50-59%** (≈60-71 points)
• 2: ~40-49%** (≈48-59 points)
• 1: below ~40% (below ~48 points)

You only need to answer ~58-60% correctly to score a 5. You can miss roughly 24 MCQ and lose 10-12 FRQ points and still earn the top score.

Morning-of checklist

• ☐ 8 hours of sleep (real sleep, not cramming).
• ☐ Real breakfast (protein + slow carbs: eggs, oatmeal, not just sugar).
• ☐ 2 sharpened #2 pencils, blue/black pens, eraser.
• ☐ Approved calculator (TI-84, TI-Nspire, etc.) + spare batteries.
• ☐ Photo ID + AP ID label sheet.
• ☐ Water bottle, snack for break (nuts, fruit).
• ☐ Watch (without alarm) if room doesn't have a clock.
• ☐ Arrive 30 minutes early.

During the exam

Multiple-choice section (60 min total)

1. Mark and skip anything that takes >90 seconds. Circle the question number and come back.
2. Process of elimination aggressively. Cross off obviously wrong answers.
3. Graph and table questions: Read the axis labels and legend twice — students misread them constantly.
4. Do not overthink. Most MCQs test one concept, not a trick.

Free-response section (90 min, 7 FRQs total: 3 long + 4 short)

1. Read all 7 questions first. Identify which are your strongest.
2. Start with your most confident FRQ. Build momentum.
3. On every part: Write the formula or integral/equation setup first, then plug in numbers.
4. Include units on every final numerical answer.
5. If stuck on (a), move to (b). Partial credit adds up. Never leave a section blank.
6. Justify with chemistry reasoning: particle behavior, IMF strength, equilibrium position shifts, spontaneity logic.

Last 5 minutes

• Skim your FRQ answers: Do they have units? Did you show setup?
• Make sure you answered each question (not just set it up).

One last thing

You've prepared. The work is done. Trust it. Show up rested, breathe between sections, and remember that the rubric wants to give you points — your job is to write clearly enough that it can.

Many students overthink on test day. If you know a formula, trust it. If you recognize an FRQ pattern you've drilled, execute it. If you don't know something, take your best guess, show your reasoning, and move on.

Good luck. You've got this. 🎯

Need more focused review? Browse the AP Chemistry topic library → or revisit the FRQ practice guide →.