PRC Chemist flashcards

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

Mole definition

One mole contains 6.022×10^23 elementary entities. Molar mass M in g/mol links mass and moles by n = m/M for stoichiometric calculations.

Ideal gas law

PV = nRT relates pressure, volume, moles, and absolute temperature. R = 8.314 J/(mol·K) or 0.08206 L·atm/(mol·K); use Kelvin always.

Limiting reagent rule

Divide moles of each reactant by its stoichiometric coefficient; the smallest quotient identifies the limiting reagent, which sets the maximum theoretical product yield.

Equilibrium constant K

K equals the product of product activities raised to coefficients divided by reactant activities. Pure solids and liquids are omitted; Q compared with K predicts direction.

Le Chatelier principle

A stressed equilibrium shifts to partly offset the change. Raising pressure favors fewer gas moles; raising temperature favors the endothermic direction; catalysts do not shift K.

Henderson-Hasselbalch equation

pH = pKa + log([A−]/[HA]) predicts buffer pH from conjugate base and acid concentrations. Buffer capacity is greatest near pH = pKa.

Nernst equation

E = E° − (RT/nF)lnQ, which at 25 °C becomes E = E° − (0.0592/n)logQ. It corrects cell potential for nonstandard concentrations.

Beer-Lambert law

A = εbc states absorbance is proportional to molar absorptivity, path length, and concentration. A = −log T; linear range is typically 0.1 to 1.0.

Equivalence point in titration

The point where titrant moles equal analyte moles by stoichiometry. For weak acid with strong base, equivalence pH exceeds 7; for weak base with strong acid it is below 7.

Primary standard criteria

A primary standard has high purity, is stable and non-hygroscopic, and has high molar mass to reduce weighing error. Examples include KHP, Na2CO3, and K2Cr2O7.

Limit of detection

LOD ≈ 3.3σ/slope and LOQ ≈ 10σ/slope, where σ is the standard deviation of blank measurements and slope comes from the calibration curve.

Chromatographic resolution

R = 2(tR2 − tR1)/(w1 + w2). Baseline separation requires R ≥ 1.5; resolution improves with greater selectivity, efficiency (N), and retention.

Gravimetric factor

Mass of analyte = mass of weighed precipitate × (M analyte / M precipitate) × coefficient ratio. Precipitate must be pure, filterable, and ignited to constant mass.

SN1 versus SN2

SN2 is one step with backside attack and inversion, favored by methyl or primary substrates and strong nucleophiles. SN1 proceeds through carbocation, favored by tertiary and polar protic solvents.

E2 elimination requirements

E2 is concerted and requires anti-periplanar geometry of leaving group and β-hydrogen. Strong bulky bases such as tert-butoxide and heat favor E2 over substitution.

Aromatic directing groups

Activating groups (–OH, –NH2, –OR, –R) direct ortho/para. Deactivating groups (–NO2, –CN, –SO3H, carbonyls) direct meta. Halogens deactivate but direct ortho/para.

CIP R/S assignment

Rank substituents by atomic number (CIP). Orient lowest priority away; clockwise is R, counterclockwise is S. Reverse if lowest priority points toward you.

Grignard addition products

RMgX adds to formaldehyde giving primary alcohol, other aldehydes giving secondary alcohols, ketones giving tertiary alcohols, esters giving tertiary alcohols, and CO2 giving carboxylic acids.

Aldol condensation

Base forms an enolate at the α-carbon, which adds to a carbonyl to give a β-hydroxy carbonyl. Heating dehydrates it to an α,β-unsaturated carbonyl.

First law of thermodynamics

ΔU = q + w. For reversible isothermal ideal-gas expansion, w = −nRT ln(V2/V1). For adiabatic processes q = 0, so ΔU equals work.

Gibbs free energy

ΔG = ΔH − TΔS. Negative ΔG indicates a spontaneous process at constant temperature and pressure; ΔG = 0 marks equilibrium.

Clausius-Clapeyron equation

ln(P2/P1) = −(ΔHvap/R)(1/T2 − 1/T1) relates vapor pressure and temperature, allowing determination of enthalpy of vaporization from two points.

Arrhenius equation

k = A e^(−Ea/RT). A plot of ln k versus 1/T is linear with slope −Ea/R, so activation energy follows from rate constants at two temperatures.

Colligative properties

ΔTb = iKbm, ΔTf = iKfm, and π = iMRT depend on particle number. The van't Hoff factor i equals ions per formula unit for strong electrolytes.

Phase rule

F = C − P + 2 gives degrees of freedom from components and phases. A pure substance at its triple point has F = 0; at the critical point liquid and gas merge.

Michaelis-Menten equation

v = Vmax[S]/(Km + [S]). Km is the substrate concentration at half-maximal velocity; low Km indicates high enzyme affinity for substrate.

Competitive inhibition

A competitive inhibitor binds the active site, raising apparent Km while leaving Vmax unchanged. Excess substrate overcomes inhibition; Lineweaver-Burk lines intersect on the y-axis.

Glycolysis net yield

One glucose yields two pyruvate, net two ATP, and two NADH. Phosphofructokinase-1 catalyzes the committed step, inhibited by ATP and activated by AMP.

DNA base pairing

Adenine pairs with thymine by two hydrogen bonds; guanine pairs with cytosine by three. Higher GC content raises melting temperature and density.

Protein structure levels

Primary is amino acid sequence, secondary is α-helix or β-sheet hydrogen bonding, tertiary is overall 3D fold, and quaternary is assembly of multiple subunits.

Haber-Bosch conditions

N2 + 3H2 gives 2NH3, exothermic. Industrial conditions are about 450 °C, 200 atm, and an iron catalyst with K2O and Al2O3 promoters; high pressure favors ammonia.

Contact process

Sulfur burns to SO2, oxidized to SO3 over V2O5 near 450 °C. SO3 is absorbed in concentrated sulfuric acid rather than water to prevent acid mist formation.

Atom economy

Atom economy = (molar mass of desired product / sum of molar masses of all reactants) × 100. It measures how much reactant mass ends up in the product.