AP Course

AP Chemistry

Updated for the AP Chemistry framework effective fall 2024, with particle models, quantitative reasoning, labs, quizzes, and practice problems.

Build general chemistry fluency through atomic structure, bonding, reactions, kinetics, equilibrium, acids and bases, thermodynamics, and electrochemistry.

Lessons

Moles and Molar MassMass Spectra of ElementsElemental Composition of Pure SubstancesComposition of MixturesAtomic Structure and Electron ConfigurationPhotoelectron SpectroscopyPeriodic TrendsValence Electrons and Ionic CompoundsTypes of Chemical BondsIntramolecular Force and Potential EnergyStructure of Ionic SolidsStructure of Metals and AlloysLewis DiagramsResonance and Formal ChargeVSEPR and HybridizationIntermolecular and Interparticle ForcesProperties of SolidsSolids, Liquids, and GasesIdeal Gas LawKinetic Molecular TheoryDeviation from Ideal Gas LawSolutions and MixturesRepresentations of SolutionsSeparation of Solutions and MixturesSolubilitySpectroscopy and the Electromagnetic SpectrumProperties of PhotonsBeer-Lambert LawIntroduction for ReactionsNet Ionic EquationsRepresentations of ReactionsPhysical and Chemical ChangesStoichiometryIntroduction to TitrationTypes of Chemical ReactionsIntroduction to Acid-Base ReactionsOxidation-Reduction (Redox) ReactionsReaction RatesIntroduction to Rate LawConcentration Changes over TimeElementary ReactionsCollision ModelReaction Energy ProfileIntroduction to Reaction MechanismsReaction Mechanism and Rate LawPre-Equilibrium ApproximationMultistep Reaction Energy ProfileCatalysisEndothermic and Exothermic ProcessesEnergy DiagramsHeat Transfer and Thermal EquilibriumHeat Capacity and CalorimetryEnergy of Phase ChangesIntroduction to Enthalpy of ReactionBond EnthalpiesEnthalpy of FormationHess’s LawIntroduction to EquilibriumDirection of Reversible ReactionsReaction Quotient and Equilibrium ConstantCalculating the Equilibrium ConstantMagnitude of the Equilibrium ConstantProperties of the Equilibrium ConstantCalculating Equilibrium ConcentrationsRepresentations of EquilibriumIntroduction to Le Châtelier’s PrincipleReaction Quotient and Le Châtelier’s PrincipleIntroduction to Solubility EquilibriaCommon-Ion EffectIntroduction to Acids and BasespH and pOH of Strong Acids and BasesWeak Acid and Base EquilibriaAcid-Base Reactions and BuffersAcid-Base TitrationsMolecular Structure of Acids and BasespH and pK_aProperties of BuffersHenderson-Hasselbalch EquationBuffer CapacitypH and SolubilityIntroduction to EntropyAbsolute Entropy and Entropy ChangeGibbs Free Energy and Thermodynamic FavorabilityThermodynamic and Kinetic ControlFree Energy and EquilibriumFree Energy of DissolutionCoupled ReactionsGalvanic (Voltaic) and Electrolytic CellsCell Potential and Free EnergyCell Potential Under Nonstandard ConditionsElectrolysis and Faraday’s Law

Quizzes

Practice Problems Equation practice, lab analysis, and FRQ-style reasoning resources can be added here.

AP Chemistry · Unit 4 · Reviewed representative lesson

Stoichiometry

Stoichiometry uses the coefficients of a balanced chemical equation as ratios between amounts in moles. The coefficients compare reacting entities; they are not direct mass ratios.

Definition

A stoichiometric coefficient states the relative number of entities and therefore the relative number of moles participating in the modeled reaction. Conservation of each element requires the equation to be balanced before any mole ratio is used.

Core Relationship

For \(aA+bB\rightarrow cC\), the amount relation is

\[\frac{n_A}{a}=\frac{n_B}{b}=\frac{n_C}{c}\]

The relation applies to reaction progress. If more than one reactant amount is given, determine which reactant limits that progress.

Worked Example

Question: Hydrogen reacts with oxygen according to \(2\mathrm{H_2}+\mathrm{O_2}\rightarrow2\mathrm{H_2O}\). With excess hydrogen, how many moles of water can form from \(3.0\,\mathrm{mol}\) of oxygen?

\[3.0\,\mathrm{mol\ O_2}\times\frac{2\,\mathrm{mol\ H_2O}}{1\,\mathrm{mol\ O_2}}=6.0\,\mathrm{mol\ H_2O}\]

Answer: \(6.0\,\mathrm{mol}\) of water can form because the balanced equation gives a 1:2 oxygen-to-water mole ratio.

Why This Method Works

The balanced equation counts conserved atoms while describing reaction events. Converting the known amount to moles makes that particle-level ratio usable; any final conversion to grams occurs only after the mole ratio.

Common Mistakes

Using coefficients before balancing the equation.
Treating coefficients as gram ratios.
Ignoring a second reactant that may be limiting.
Rounding intermediate results so early that the final answer shifts.

Key Takeaways

Balance first, convert to moles, apply one mole ratio, then convert to the requested unit.
The limiting reactant sets the maximum product amount.
Units should cancel at every conversion step.

Practice connection

Use the quiz and practice tabs to extend the mole-ratio workflow to mass, solution, and limiting-reactant questions.

Official curriculum reference: College Board AP Chemistry course page. The explanation and worked example are independently written for this study site.