MCAT Chem/Phys flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature, with R = 0.0821 L·atm/(mol·K). Use it to solve for any one variable when the other three are known.

pH of strong acid

For a monoprotic strong acid of concentration C, [H3O+] approximately equals C and pH = −log C. A strong base of concentration C gives pOH = −log C.

Henderson–Hasselbalch equation

pH = pKa + log([A−]/[HA]) gives the pH of a buffer. When [A−] equals [HA], pH equals pKa, so buffers work best within one pH unit of pKa.

Gibbs free energy equation

ΔG° = −RT ln K = ΔH° − TΔS°. A negative ΔG means the reaction is spontaneous as written; ΔG equals zero at equilibrium, where Q = K.

Le Châtelier's principle

When a system at equilibrium is disturbed by a change in concentration, pressure, or temperature, it shifts in the direction that partially counteracts that disturbance.

First-order half-life

For a first-order reaction, t1/2 = ln2/k ≈ 0.693/k, independent of starting concentration. For a zero-order reaction, t1/2 = [A]0/(2k).

Colligative properties formulas

ΔTb = iKb·m and ΔTf = −iKf·m depend on the number of dissolved particles, not their identity. Osmotic pressure is π = iMRT, where i is the van't Hoff factor.

Michaelis–Menten equation

v = Vmax[S]/(Km + [S]). Km is the substrate concentration at half-maximal velocity and reflects apparent enzyme–substrate affinity, so a lower Km means tighter binding.

Competitive inhibition effect

A competitive inhibitor binds the active site, raising apparent Km while leaving Vmax unchanged, because sufficiently high substrate concentration can outcompete the inhibitor.

Net ATP from glycolysis

One glucose yields two pyruvate, a net of 2 ATP, and 2 NADH. The committed, rate-limiting step is catalyzed by phosphofructokinase-1 (PFK-1).

TCA cycle products

Per acetyl-CoA, the citric acid cycle produces 3 NADH, 1 FADH2, 1 GTP, and 2 CO2. The cycle occurs in the mitochondrial matrix.

Isoelectric point rule

At a pH below its pI, a molecule is protonated and positively charged; above its pI it is deprotonated and negatively charged; at the pI net charge is zero.

Hemoglobin versus myoglobin

Hemoglobin binds O2 cooperatively, giving a sigmoidal curve, and is right-shifted by H+, CO2, and 2,3-BPG. Myoglobin binds noncooperatively with a hyperbolic curve.

β-oxidation yield

For a saturated fatty acid with n carbons, β-oxidation gives n/2 acetyl-CoA, (n/2 − 1) NADH, and (n/2 − 1) FADH2 before the acetyl-CoA enters the TCA cycle.

Kinematic equations

v = v0 + at, x = x0 + v0t + ½at², and v² = v0² + 2aΔx apply when acceleration is constant; choose the equation that omits the unknown you do not need.

Work–energy theorem

The net work done on an object equals its change in kinetic energy, Wnet = ΔKE. With no nonconservative forces, kinetic plus potential energy remains constant.

Momentum conservation

In an isolated system, total momentum p = mv is conserved in every collision. Kinetic energy is conserved only in elastic collisions; perfectly inelastic collisions lose the most kinetic energy.

Buoyant force

Archimedes' principle: buoyant force equals the weight of displaced fluid, Fb = ρfluid·Vdisplaced·g. An object floats when its average density is less than the fluid's density.

Snell's law

n1·sinθ1 = n2·sinθ2 describes refraction at an interface. Total internal reflection occurs going from higher to lower n when the incident angle exceeds θc, where sinθc = n2/n1.

Resistors in parallel

Parallel resistors share the same voltage, and their equivalent resistance satisfies 1/Req = 1/R1 + 1/R2 + …, so Req is smaller than the smallest individual resistor.

Hybridization and geometry

Four electron groups give sp3 and tetrahedral 109.5°; three give sp2 and trigonal planar 120°; two give sp and linear 180°. A lone pair counts as one group.

Hückel aromaticity rule

Aromatic rings are cyclic, planar, fully conjugated, and contain 4n + 2 π electrons. Rings with 4n π electrons are antiaromatic; nonplanar or nonconjugated rings are nonaromatic.

SN2 reaction conditions

SN2 is a one-step backside displacement with inversion of configuration, favored by methyl or primary substrates, strong nucleophiles, and polar aprotic solvents such as DMSO or acetone.

SN1 versus E1

Both proceed through a carbocation, so both are favored by tertiary substrates and polar protic solvents. SN1 gives substitution with racemization; E1 gives an alkene and is favored by heat.

Infrared carbonyl stretch

A strong C=O stretch near 1700 cm−1 indicates a ketone, aldehyde, ester, or carboxylic acid; O–H appears broad at 3200–3600 cm−1 and N–H near 3300 cm−1.

NMR n+1 splitting rule

A proton signal splits into n + 1 peaks by n equivalent neighboring protons. Integration gives relative proton counts, and downfield signals at higher ppm are more deshielded.

Central dogma

DNA is transcribed to mRNA by RNA polymerase and translated to protein by ribosomes. Replication is semiconservative, and new DNA strands grow in the 5′ to 3′ direction.

Mitosis versus meiosis

Mitosis yields two genetically identical diploid cells. Meiosis has one replication followed by two divisions and yields four haploid, genetically distinct gametes.

Dihybrid cross ratio

For two unlinked genes showing independent assortment and complete dominance, a cross of double heterozygotes produces a 9:3:3:1 phenotypic ratio in the offspring.

Na+/K+ ATPase action

This primary active transporter uses one ATP to move 3 Na+ out of the cell and 2 K+ in, maintaining the resting membrane potential and driving secondary active transport.

Hardy–Weinberg conditions

Allele frequencies stay constant only with no mutation, no migration, no selection, infinite population size, and random mating; genotype frequencies are p² + 2pq + q² = 1.

Steroid versus peptide hormones

Steroid hormones are lipid-soluble, cross the membrane, and bind intracellular receptors to alter transcription. Peptide hormones bind surface receptors and act through second messengers.