MCAT General Chemistry: Complete Topic Guide (2026)

General chemistry appears primarily in the Chem/Phys section but also surfaces in Bio/Biochem (buffer systems, enzyme kinetics, electrochemistry in biological contexts). Here's every major gen chem topic the MCAT tests, ranked by importance.

Tier 1: Appears on Almost Every MCAT

Acids, Bases, and Buffers

This is the single highest-yield gen chem topic. Know:

• Brønsted-Lowry and Lewis definitions
• pH = -log[H⁺], pOH = -log[OH^-], pH + pOH = 14
• Henderson-Hasselbalch: pH = pK_a + log([A^-]/[HA])
• Strong vs. weak acids/bases and their conjugates
• Buffer capacity and how buffers resist pH change
• Titration curves: equivalence point, half-equivalence point (pH = pK_a), buffer region

The MCAT loves combining acid-base chemistry with biochemistry — amino acid titration curves, blood buffering (bicarbonate system), and enzyme pH optima are all fair game.

Thermodynamics

Key equations and concepts:

• ΔG = ΔH - TΔS (Gibbs free energy — memorize this)
• ΔG < 0 = spontaneous, ΔG > 0 = non-spontaneous
• ΔG°' = -RT ln(K_eq)
• Hess's law: ΔH_rxn = ΣΔH_f(products) - ΣΔH_f(reactants)
• Entropy: disorder, S increases with temperature, phase changes, dissolving
• Coupled reactions: how ATP hydrolysis drives non-spontaneous reactions

Chemical Equilibrium

• K_eq expression, reaction quotient Q, and Le Chatelier's principle
• K_sp (solubility product) — common ion effect, predicting precipitation
• Relationship between K and ΔG°
• How temperature, pressure, and concentration affect equilibrium

Chemical Kinetics

• Rate laws: rate = k[A]^m[B]ⁿ
• Zero, first, and second order reactions: integrated rate laws, half-life formulas
• Arrhenius equation: k = Ae^-E_a/RT
• Catalysts lower E_a but don't change ΔG or K_eq
• Energy diagrams: transition state, intermediate, activation energy

Tier 2: Appears on Most MCATs

Electrochemistry

• Galvanic vs. electrolytic cells
• E°_cell = E°_cathode - E°_anode
• ΔG° = -nFE°
• Nernst equation: E = E° - (RT/nF)ln(Q)
• Oxidation at anode, reduction at cathode (mnemonic: An Ox, Red Cat)
• Standard reduction potentials and predicting spontaneity

Atomic Structure and Periodic Trends

• Electron configuration, quantum numbers, orbital filling order
• Periodic trends: electronegativity, ionization energy, atomic radius, electron affinity
• Effective nuclear charge (Z_eff) explains most trends
• Transition metal electron configurations and exceptions (Cr, Cu)

Bonding and Molecular Structure

• Ionic vs. covalent vs. metallic bonding
• Lewis structures, formal charge, resonance
• VSEPR theory and molecular geometry
• Hybridization: sp, sp², sp³
• Intermolecular forces: London dispersion, dipole-dipole, hydrogen bonding
• Polarity and its effects on solubility and boiling point

Solutions and Colligative Properties

• Molarity, molality, mole fraction, dilution (M₁V₁ = M₂V₂)
• Colligative properties: boiling point elevation, freezing point depression, osmotic pressure
• π = iMRT (van't Hoff equation for osmotic pressure)
• "Like dissolves like" — polar solvents dissolve polar solutes

Tier 3: Shows Up Periodically

Gas Laws

• PV = nRT (ideal gas law)
• Dalton's law of partial pressures
• Graham's law of effusion
• Real gases: van der Waals equation and deviations from ideal behavior

Nuclear Chemistry

• α, β, γ decay and their properties
• Half-life calculations (first-order kinetics)
• Mass-energy equivalence: E = mc²

Redox Reactions

• Oxidation states and how to assign them
• Balancing redox reactions (half-reaction method)
• Common oxidizing and reducing agents

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