High-Yield MCAT Chem/Phys Topics — General Chem, Organic, Physics & Thermodynamics

The Chemical and Physical Foundations of Biological Systems section — usually shortened to Chem/Phys — is one of four scored sections on the MCAT, alongside Critical Analysis and Reasoning Skills (CARS), Biological and Biochemical Foundations of Living Systems (Bio/Biochem), and Psychological, Social, and Biological Foundations of Behavior (Psych/Soc). The MCAT is administered by the Association of American Medical Colleges (AAMC).

What makes Chem/Phys distinctive is that it blends four disciplines into a single passage-based section: general chemistry, physics, organic chemistry, and a layer of biochemistry. The AAMC does not recycle exact questions from one exam to the next, so there is no such thing as a bank of "repeated" questions to memorize. What does repeat is the set of high-yield concepts the test rewards you for understanding deeply. This guide walks through those concepts by discipline so you know where to invest your study time.

Each section is scored on a scale of 118 to 132, and the four section scores combine into a total that ranges from 472 to 528, centered at 500. Because Chem/Phys questions are mostly reasoning-based rather than recall-based, mastering the underlying principles below matters far more than trying to memorize answers.

How the Chem/Phys Content Breaks Down

The AAMC organizes the exam around foundational concepts and content categories rather than a fixed number of questions per topic. Still, it helps to know the relative emphasis so you can prioritize. Here is an approximate breakdown of where the concepts cluster:

Notice that acids/bases, thermodynamics, and fluids carry outsized weight because they connect directly to physiology — buffering in blood, energetics of metabolism, and pressure and flow in the circulatory and respiratory systems. Master these first.

General Chemistry

General chemistry on the MCAT is less about rote calculation and more about reasoning through what happens to a system when you change a variable. The high-yield areas are stoichiometry, acid-base chemistry, equilibrium, kinetics, and electrochemistry.

Stoichiometry and Solutions

You should be fluent in mole conversions, limiting reagents, percent yield, and empirical versus molecular formulas. Solution chemistry adds molarity, dilution (M₁V₁ = M₂V₂), and colligative properties such as boiling-point elevation and freezing-point depression. Expect to interpret titration curves and read data straight from a passage rather than plug into a memorized formula.

Acids, Bases, and Buffers

This is one of the highest-yield topics in the entire section. Know the difference between strong and weak acids, how to calculate pH from [H⁺] (pH = −log[H⁺]), and how the Henderson-Hasselbalch equation (pH = pK⁵ + log([A⁻]/[HA])) predicts buffer behavior. A buffer resists pH change and is most effective when pH is within about one unit of the pK⁵. The bicarbonate buffer system in blood is a favorite biological application.

Chemical Equilibrium

Understand the equilibrium constant (K), the reaction quotient (Q), and how comparing Q to K tells you which direction a reaction will shift. Le Chatelier's principle predicts how a system at equilibrium responds to changes in concentration, pressure, volume, or temperature. Remember that a catalyst speeds the approach to equilibrium but does not change the position of equilibrium or the value of K.

Reaction Kinetics

Kinetics describes how fast a reaction proceeds, which is independent of thermodynamics (how far it goes). Be comfortable determining rate laws and reaction order from experimental data, and know that the rate-determining step is the slowest step. The Arrhenius relationship shows that raising temperature or lowering activation energy (for example, with an enzyme or catalyst) increases the rate.

Electrochemistry

Know the distinction between galvanic (spontaneous, powers a device) and electrolytic (non-spontaneous, requires an external source) cells, and that oxidation always occurs at the anode and reduction at the cathode in both. A positive standard cell potential corresponds to a spontaneous reaction and a negative Gibbs free energy, linking electrochemistry directly to thermodynamics.

Organic Chemistry

Organic chemistry on the MCAT is streamlined compared with a full undergraduate course. The test emphasizes recognizing functional groups, predicting the outcome of common reactions, understanding key mechanisms, and interpreting spectra — all in a biochemistry-flavored context.

Functional Groups and Nomenclature

Be able to instantly recognize alcohols, aldehydes, ketones, carboxylic acids, esters, amides, amines, and ethers, and know their relative reactivity and physical properties (for example, why carboxylic acids boil higher than aldehydes of similar mass). Reactivity trends among carbonyl-containing compounds are especially high-yield.

Mechanisms and Stereochemistry

Focus on the mechanisms that appear most often: nucleophilic addition to carbonyls, nucleophilic acyl substitution, and the SN1/SN2 and E1/E2 pathways. Know how sterics and carbocation stability decide whether a reaction goes SN1 or SN2. Stereochemistry — chirality, enantiomers versus diastereomers, R/S designation, and the concept of optical activity — comes up regularly because biological molecules are chiral.

Biologically Relevant Reactions

Because Chem/Phys blends in biochemistry, prioritize reactions that show up in metabolism: esterification and hydrolysis, oxidation and reduction of alcohols and carbonyls, and the formation and cleavage of amide (peptide) bonds. Understanding these in a mechanistic sense helps on both this section and Bio/Biochem.

Spectroscopy and Separations

You are expected to interpret rather than derive spectra. For infrared (IR) spectroscopy, recognize characteristic absorptions such as the broad O–H of alcohols and the sharp C=O of carbonyls. For ¹H NMR, understand chemical shift, splitting (n+1 rule), and integration. Also know the logic behind separation techniques such as chromatography, distillation, and extraction.

Physics

MCAT physics rewards conceptual understanding and dimensional reasoning far more than heavy calculation. Most problems can be solved by identifying the right relationship and reasoning about how variables scale. The high-yield areas are kinematics, forces, energy, fluids, circuits, and optics.

Kinematics and Forces

Know the kinematic equations for constant acceleration, the difference between scalars and vectors, and how to resolve vectors into components. Newton's three laws underpin force problems: draw a free-body diagram, sum the forces, and apply F = ma. Common setups include inclined planes, tension, friction, and circular motion (centripetal force).

Work, Energy, and Momentum

Understand the work-energy theorem, conservation of mechanical energy, and how kinetic and potential energy interconvert. Power is the rate of doing work. For collisions, apply conservation of momentum, and distinguish elastic collisions (kinetic energy conserved) from inelastic ones (kinetic energy not conserved).

Fluids and Gases

Fluids are among the most tested physics topics because of their physiological relevance. Master hydrostatic pressure (P = ρgh), buoyancy and Archimedes' principle, the continuity equation (A₁v₁ = A₂v₂), and Bernoulli's principle relating pressure and flow velocity. Poiseuille's law and the concept of resistance to flow connect directly to blood pressure and circulation.

Circuits and Electrostatics

Know Coulomb's law and the concept of electric fields, then apply Ohm's law (V = IR) and the rules for combining resistors and capacitors in series and parallel. Power dissipation (P = IV = I²R) is a frequent question. Circuit reasoning also underlies the physics of neurons and membrane potentials.

Waves, Sound, and Optics

Understand wave properties (frequency, wavelength, amplitude), the Doppler effect, and resonance. In optics, know reflection and refraction (Snell's law), total internal reflection, and image formation with the thin-lens and mirror equations. These principles appear in questions about hearing, vision, and medical imaging.

Thermodynamics

Thermodynamics sits at the intersection of chemistry and physics and is one of the most conceptually important areas of the section because it governs whether processes happen spontaneously.

The Laws and State Functions

The first law is conservation of energy (ΔU = q + w). Recognize that enthalpy (H), entropy (S), internal energy (U), and Gibbs free energy (G) are state functions — they depend only on the initial and final states, not the path taken. Hess's law follows directly: the enthalpy change of a reaction is the same regardless of how many steps it takes.

Enthalpy and Entropy

Exothermic reactions release heat and have a negative ΔH; endothermic reactions absorb heat and have a positive ΔH. Entropy measures disorder or the dispersal of energy, and the second law states that the entropy of the universe increases for any spontaneous process.

Gibbs Free Energy and Spontaneity

The single most important equation here is ΔG = ΔH − TΔS. A negative ΔG indicates a spontaneous (exergonic) process; a positive ΔG indicates a non-spontaneous (endergonic) one. Because the temperature term multiplies entropy, whether a reaction is spontaneous can flip depending on temperature. This framework explains how cells couple unfavorable reactions to favorable ones such as ATP hydrolysis.

How to Study for MCAT Chem/Phys

Because Chem/Phys is reasoning-heavy and content-broad, effective preparation looks different from cramming facts. Here are proven strategies:

1. Use AAMC materials as your gold standard. The AAMC section banks, question packs, and official full-length practice exams most closely match the real test's style and difficulty. Save some for realistic timed practice as your test date approaches.
2. Supplement with third-party question banks. Resources such as UWorld are widely used for their detailed explanations and passage-style questions. Review courses and books from Kaplan and The Princeton Review provide structured content review, and Khan Academy's archived MCAT collection remains a solid free foundation.
3. Prioritize the high-yield connectors. Acids/bases and buffers, thermodynamics and Gibbs free energy, and fluids each link chemistry or physics to physiology. Deep understanding of these pays off across multiple sections.
4. Practice with passages, not just discrete questions. Most Chem/Phys questions are embedded in research-style passages. Train yourself to extract relevant data quickly and ignore the noise.
5. Reason by proportionality and dimensional analysis. Check the units of your answer and think about how variables scale. This eliminates wrong options fast and often replaces lengthy calculation.
6. Build a formula and concept sheet. Keep a running one-page sheet of key relationships (kinematics equations, Henderson-Hasselbalch, ΔG = ΔH − TΔS, Bernoulli, Ohm's law) and review it regularly rather than re-deriving each time. Our free MCAT chemistry notes and physics notes summarize these relationships by topic.
7. Review every miss thoroughly. For each wrong answer, identify whether it was a content gap, a reasoning error, or a careless mistake. Thoughtful review of your practice is where most score gains come from.
8. Simulate test conditions. Take timed, full-length practice exams to build stamina and pacing, since the real MCAT is a long day and endurance matters as much as knowledge.