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 5 · Topic 5.9

Pre-Equilibrium Approximation

Collision frequency, orientation, activation energy, and mechanisms explain measured rate laws.

1. Topic Lens

Pre-Equilibrium Approximation is studied through kinetics. Connect the system boundary, interacting parts, and measurable evidence before applying a formula.

\[rate=k[A]^m[B]^n\]

Chemical equation or molecular relation

\[2NO_2\rightarrow2NO+O_2\]

2. Why the Formula Works

The relationship is built from definitions and conservation reasoning:

Experiments reveal how rate responds to concentration; coefficients alone do not determine orders for an overall reaction.
Take logarithms to convert the multiplicative rate law to an additive relationship.
Slopes or trial ratios determine orders, while the intercept contains k.

\[\ln(\text{rate})=\ln k+m\ln[A]+n\ln[B]\]

3. Detailed Visual Model

Pre-Equilibrium Approximation: an original pixel-style model. Use it as a schematic, not a literal scale drawing.

4. Worked Example and Lab Link

Doubling [A] quadruples the rate while [B] is fixed. What is the order in A?

Answer: Because 2^m=4, m=2; the reaction is second order in A.

Investigation idea: Use original concentration-time data to determine initial rates and test candidate rate laws.

Common trap: Reaction orders are experimental unless the step is explicitly elementary; a catalyst does not change equilibrium K.

Checkpoint · Topic 5.9

Explain how pre-equilibrium approximation supports or limits this conclusion: Because 2^m=4, m=2; the reaction is second order in A.

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