Getting Ahead: AP Chemistry

Master atoms, reactions, and thermodynamics. Get ready to earn that 5!

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📝 AP Exam Breakdown

The AP Chemistry exam is 3 hours and 15 minutes long and has two sections.

Section Question Type # of Questions Time % of Score
Section I Multiple Choice 60 questions 1 hour 30 minutes 50%
Section II Long Free Response 3 questions 1 hour 45 minutes 50%
Short Free Response 4 questions

📘 Core Units You'll Learn

🔬 Key Formulas

Ideal Gas Law
PV = nRT
P = pressure, V = volume, n = moles, R = gas constant, T = temperature (K)
Density of a Gas
d = PM / RT
d = density, P = pressure, M = molar mass, R = gas constant, T = temperature (K)
Dilution Equation
M₁V₁ = M₂V₂
M = molarity, V = volume; subscripts 1 and 2 refer to initial and final conditions
Specific Heat / Calorimetry
q = mcΔT
q = heat, m = mass, c = specific heat capacity, ΔT = change in temperature
Enthalpy via Hess's Law
ΔH°rxn = ΣΔH°f(products) − ΣΔH°f(reactants)
Standard enthalpy of reaction from standard enthalpies of formation
Gibbs Free Energy
ΔG° = ΔH° − TΔS°
ΔG° = standard free energy, ΔH° = enthalpy, T = temperature (K), ΔS° = entropy
Relationship of ΔG° and K
ΔG° = −RT ln K
Connects standard free energy change to the equilibrium constant
Nernst Equation
E = E° − (RT / nF) ln Q
E = cell potential, E° = standard cell potential, n = moles of electrons, F = Faraday's constant, Q = reaction quotient
Rate Law
Rate = k[A]m[B]n
k = rate constant, [A] and [B] = reactant concentrations, m and n = reaction orders
Arrhenius Equation
k = Ae−Ea/RT
k = rate constant, A = frequency factor, Ea = activation energy, R = gas constant, T = temperature (K)
pH and pOH
pH = −log[H⁺]   |   pOH = −log[OH⁻]
pH + pOH = 14 at 25°C
Henderson-Hasselbalch Equation
pH = pKa + log([A⁻] / [HA])
Used to calculate the pH of a buffer solution
Equilibrium Expression
Kc = [products]coefficients / [reactants]coefficients
Kc for concentrations; Kp for partial pressures; Kp = Kc(RT)Δn
Energy of a Photon
E = hν = hc / λ
E = energy, h = Planck's constant, ν = frequency, c = speed of light, λ = wavelength
de Broglie Wavelength
λ = h / mv
λ = wavelength, h = Planck's constant, m = mass, v = velocity
Coulomb's Law
F = k · q₁q₂ / r²
F = force, k = Coulomb's constant, q = charges, r = distance between charges
💡 Study Tip

Focus on understanding the Big Ideas that connect all nine units: scale, proportion, and quantity; structure and properties; transformations; and energy. Practice free-response questions regularly and always show your work with proper units and significant figures. Using dimensional analysis consistently will keep your calculations organized and help you avoid common mistakes on the AP exam.

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