OpenStem

@openstem · Joined Jul 2026

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According to kinetic molecular theory, what is true about the AVERAGE kinetic energy of different gases at the same temperature?1 / 10

All gases at the same temperature have the same average translational kinetic energy, regardless of their identity or molar mass: KE_avg = (3/2)RT, which depends only on T. Since KE = ½mv², a heavier molecule (larger m) must have a proportionally smaller average v² to keep KE the same as a lighter molecule's — heavier molecules simply move slower, on average, at a given temperature.

Chemistry

Chemistry · L4 · Effusion, Diffusion & Graham's Law

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Distinguish a homogeneous equilibrium from a heterogeneous equilibrium.1 / 10

In a homogeneous equilibrium, every reactant and product is in the SAME phase (e.g. all gases, or all species dissolved in the same solution). In a heterogeneous equilibrium, the reactants and products span TWO OR MORE phases — commonly a solid or pure liquid coexisting with gases or with species in solution, such as CaCO₃(s) ⇌ CaO(s) + CO₂(g).

Chemistry

Chemistry · L4 · Heterogeneous Equilibria & Kp

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Describe electron impact (EI) ionization, and identify the species produced first — the molecular ion.1 / 10

In EI, the vaporised sample is bombarded with a high-energy electron beam (typically ~70 eV) that knocks a single electron out of a neutral molecule M, producing a radical cation M⁺• — the molecular ion. It's called a radical cation because it carries both a positive charge and an unpaired electron. Its mass-to-charge ratio, m/z, equals the compound's nominal molecular weight (since the mass lost as one electron is negligible).

Chemistry

Chemistry · L4 · Mass Spectrometry: EI Fragmentation Patterns

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What is retrosynthetic analysis, and which direction does its disconnection arrow (⇒) point?1 / 10

Retrosynthetic analysis works BACKWARDS from a target molecule toward simpler, ideally commercially available starting materials, by mentally breaking (disconnecting) bonds one at a time. The disconnection arrow ⇒ points from the more complex target to the simpler precursor(s) — the opposite direction from an actual forward reaction arrow (→), which is why the same route is drawn once backwards (planning) and once forwards (the real synthesis).

Chemistry

Chemistry · L4 · Organic Synthesis Routes & Retrosynthetic Analysis

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List the six steps of the half-reaction (ion-electron) method for balancing a redox equation in ACIDIC solution.1 / 10

(1) Split the skeleton equation into an oxidation half-reaction and a reduction half-reaction. (2) Balance all atoms EXCEPT O and H in each half-reaction. (3) Balance O by adding H₂O. (4) Balance H by adding H⁺. (5) Balance charge by adding electrons (e⁻) to the more positive side. (6) Multiply each half-reaction by whatever factor makes the electrons lost equal the electrons gained, then add the two half-reactions together, cancelling anything that appears identically on both sides.

Chemistry

Chemistry · L4 · Balancing Redox Equations & Redox Titrations

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State the calorimetry equation q = mcΔT and define every symbol.1 / 10

q is the heat transferred (J or kJ), m is the mass of the substance (g), c is its specific heat capacity (J/(g·°C), an intensive property specific to the material), and ΔT is the temperature change, T_final − T_initial (°C or K — the size of a degree is the same on both scales, so ΔT is identical either way).

Chemistry

Chemistry · L4 · Thermochemistry: Calorimetry Calculations

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State the LCAO (Linear Combination of Atomic Orbitals) approximation for a diatomic molecule.1 / 5

A molecular orbital ψ is approximated as a linear combination of atomic orbitals χᵢ on each nucleus:

Chemistry

Chemistry · L5 · Quantum Chemistry & MO Theory

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Contrast SN2 and SN1 mechanisms: kinetics, stereochemistry, and substrate effects.1 / 5

SN2: bimolecular, rate = k[substrate][nucleophile], proceeds via a single concerted back-side attack transition state → complete inversion of configuration (Walden inversion). Favoured by primary substrates and strong nucleophiles in polar aprotic solvents.

Chemistry

Chemistry · L5 · Advanced Organic Mechanisms & Retrosynthesis

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State the Boltzmann distribution law for two states i and j. What does it imply about the population of higher-energy states as temperature decreases?1 / 9

In thermal equilibrium at temperature T, the ratio of populations Nᵢ and Nⱼ of two states with energies Eᵢ and Eⱼ (degeneracies gᵢ, gⱼ) is:

Chemistry

Chemistry · L5 · Statistical Thermodynamics

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State the spectrochemical series ranking of common ligands from weakest to strongest field, as used to predict Δo.1 / 10

I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN⁻ ≈ CO (strongest field). Roughly, this tracks σ-donor/π-acceptor character: the halides are π-donors that push t2g energy up (shrinking Δo), NH₃ and en are pure σ-donors sitting in the middle, and CN⁻/CO are strong π-acceptors that pull t2g energy down by accepting metal electron density into empty π* orbitals (back-bonding), which widens Δo.

Chemistry

Chemistry · L5 · Ligand Field Theory

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State the 18-electron rule and the analogy it is based on.1 / 9

A transition-metal complex tends to be especially stable when the metal's total valence electron count — its own d-electrons plus every electron donated by its ligands — reaches 18, filling all nine valence orbitals (one s, three p, five d). It is the organometallic analogue of the main-group octet rule (one s + three p = 8). Fe(CO)5, Ni(CO)4, Cr(CO)6, and ferrocene all obey it exactly, but it is a strong guideline, not an absolute law — plenty of stable complexes sit below 18.

Chemistry

Chemistry · L5 · Organometallic Chemistry: Electron Counting & Elementary Steps

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What is the central goal of computational chemistry?1 / 10

To find approximate solutions to the electronic Schrödinger equation for a real, many-electron molecule — cheaply enough to actually run on a computer — in order to predict structure (geometry), energy (reaction energetics, barriers), and other properties (spectra, dipole moments) without needing a closed-form exact solution, which exists only for one-electron systems.

Chemistry

Chemistry · L5 · Computational Chemistry & DFT Basics

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What distinguishes outer-sphere from inner-sphere electron transfer?1 / 10

In outer-sphere ET, donor and acceptor never form a bond — the electron tunnels across the gap during a brief close approach, and both species keep their original coordination spheres intact. In inner-sphere ET, a ligand bridges the two metal centres (bond forms, then breaks), as in Taube's classic Cr²⁺ + Co(NH₃)₅Cl²⁺ chloride-bridged experiment. Marcus theory in its simplest form treats outer-sphere transfer.

Chemistry

Chemistry · L5 · Marcus Theory & Electron Transfer Kinetics

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What physically happens to a polymer's chains at the glass transition temperature Tg?1 / 7

Below Tg, chains are effectively frozen — only small-scale vibrational and local bond motion is possible, not large-scale segmental motion, so the bulk material is a rigid glass. At and above Tg, the free volume between chains grows enough that cooperative segmental motion becomes accessible: chain segments can wiggle past one another, and the material turns rubbery or leathery.

Chemistry

Chemistry · L5 · Tg, Tm & Crystallinity

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Why does linear HDPE pack into a more crystalline, denser solid than branched LDPE, even though both are polyethylene?1 / 7

HDPE's chains are essentially unbranched, so they lie parallel to one another and fold into tightly packed, ordered lamellae. LDPE's frequent short- and long-chain branches stick out sideways and physically block that regular packing, forcing more of the material into disordered amorphous regions — lower crystallinity, lower density.

Chemistry

Chemistry · L5 · Chain Structure → Bulk Properties

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Flashcards6 cards

Why is a 2D NMR experiment needed for a complex molecule when 1D ¹H NMR already gives chemical shifts and coupling patterns?1 / 6

For a molecule with many similar protons, a 1D spectrum gets too crowded — peaks overlap and individual couplings become impossible to read out. A 2D experiment spreads the same information across two frequency axes instead of one, so each correlation gets its own point in a plane rather than competing for space on a single line. This resolves overlap and directly reveals WHICH nuclei are related to which, rather than just listing shifts and multiplicities.

Chemistry

Chemistry · L5 · 2D NMR: COSY & HSQC

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What does the Karplus equation relate, in general terms?1 / 6

It relates the vicinal (three-bond, ³J) H–H coupling constant to the dihedral (torsion) angle θ between the two coupled C–H bonds: ³J(θ) = A cos²θ + B cosθ + C, where A, B, C are empirically fit constants. Measuring ³J therefore lets you estimate θ, and so probe 3D geometry rather than just connectivity.

Chemistry

Chemistry · L5 · Karplus Equation & Coupling-Constant Analysis

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What does a Jablonski diagram depict?1 / 8

A Jablonski diagram maps the electronic and vibrational energy levels a molecule can occupy after absorbing a photon, and every pathway back down: fluorescence, intersystem crossing, phosphorescence, and non-radiative decay. Vertical position represents energy; singlet states (S₀, S₁, S₂, …) and triplet states (T₁, T₂, …) are drawn as separate manifolds because they differ in spin multiplicity.

Chemistry

Chemistry · L5 · Photochemistry

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How did Jean-Marie Lehn define supramolecular chemistry, and how does it differ from ordinary molecular chemistry?1 / 8

Lehn described supramolecular chemistry as "chemistry beyond the molecule" — the study of organized entities (supermolecules and assemblies) held together not by covalent bonds but by non-covalent intermolecular forces. Where molecular chemistry is the chemistry of the covalent bond, supramolecular chemistry is the chemistry of molecular recognition, self-assembly, and reversible binding between complementary partners.

Chemistry

Chemistry · L5 · Supramolecular Chemistry: Foundations

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State Cram's preorganization principle.1 / 7

The more a host's binding sites are already arranged — both sterically and electronically — to complement a given guest before binding occurs, the stronger and more selective the resulting complex will be. A highly preorganized host pays little conformational or entropic 'cost' to reach its binding geometry, because it is already there.

Chemistry

Chemistry · L5 · Supramolecular Chemistry: Preorganization & Design

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Define the E-factor. What do very high or very low values mean?1 / 10

E-factor = mass of waste / mass of product (kg waste per kg product isolated). An E-factor of 0 is the unreachable ideal — every input atom ends up in the product. A high E-factor means the process generates many kilograms of waste — solvents, byproducts, purification losses — for every kilogram of product actually isolated; the higher the number, the further the real process is from ideal.

Chemistry

Chemistry · L5 · Green Chemistry — Sustainable Catalysis

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Enzyme catalysis follows the mechanism E + S ⇌ ES → E + P. Which approximation from the generic two-step mechanism (A ⇌ I → P) applies directly here, and to which species?1 / 12

The steady-state approximation, applied to the enzyme-substrate complex ES — exactly as you set d[I]/dt ≈ 0 for a generic intermediate I, here you set d[ES]/dt ≈ 0.

Chemistry

Chemistry · L5 · Enzyme Kinetics

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What are the core assumptions of the Langmuir adsorption model?1 / 10

(i) The surface has a fixed number of adsorption sites, all identical; (ii) each site can hold at most one adsorbed molecule — strictly a monolayer, with no stacking of further molecules on top; (iii) sites are independent and non-interacting — occupying one site neither helps nor hinders adsorption at a neighbouring site.

Chemistry

Chemistry · L5 · Surface Chemistry and Adsorption

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State the third law of thermodynamics. Why does it single out a perfect crystal?1 / 10

The entropy of a perfectly ordered, pure crystalline substance approaches zero as the temperature approaches absolute zero:

Chemistry

Chemistry · L5 · The Third Law and Absolute Entropy

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Give the formula for the crystal field stabilization energy (CFSE) of an octahedral complex in terms of the number of electrons in t2g and eg.1 / 11

n(t2g) and n(eg) are the electron counts in the lower and upper octahedral sets. Each t2g electron is stabilized by 0.4Δo (often written −2/5 Δo) below the barycenter, and each eg electron is destabilized by 0.6Δo (+3/5 Δo) above it — the two sets are weighted so the barycenter (average energy if the five d-orbitals were degenerate) is preserved: 3×(−0.4) + 2×(+0.6) = 0.

Chemistry

Chemistry · L5 · Crystal Field Stabilization Energy

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Why does conventional free-radical polymerization produce a broad molecular-weight distribution (high dispersity, PDI)?1 / 10

Initiator molecules decompose randomly throughout the reaction, so individual chains initiate at staggered times — some start growing early, some start late. Propagating radicals also terminate irreversibly and at random (by coupling or disproportionation) whenever two radical chain ends happen to collide. Because both initiation and termination are random events spread across the whole reaction time, chains end up wildly different lengths, giving a broad, high-PDI molecular-weight distribution.

Chemistry

Chemistry · L5 · Controlled and Living Polymerization

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A chiral bidentate phosphine like BINAP replaces PPh3 in a Wilkinson's-type hydrogenation catalyst. Which elementary steps of the catalytic cycle stay exactly the same?1 / 12

The same skeleton as the achiral Wilkinson's cycle: ligand dissociation to open a site, oxidative addition of H2, alkene association, migratory insertion of the alkene into a Rh–H bond, and reductive elimination to release the alkane and regenerate the active catalyst. Nothing about those five steps changes — what changes is the shape of the ligand sitting on the metal throughout all of them.

Chemistry

Chemistry · L5 · Asymmetric Catalysis Mechanisms

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What is a Schottky defect?1 / 12

A matched pair of vacancies in an ionic lattice — one cation site and one anion site are both left empty. Because equal numbers of positive and negative ions are removed, overall electroneutrality of the crystal is preserved.

Chemistry

Chemistry · L5 · Crystal Defects and Semiconductors

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What causes the small M+1 peak in a mass spectrum, and roughly how big is it?1 / 12

The M+1 peak arises mainly from the natural abundance of heavier isotopes, dominated by ¹³C (~1.1% of all carbon atoms, versus ~98.9% ¹²C). Each carbon in the molecule contributes about 1.1% to the M+1 peak's height relative to M, so for a compound with N carbon atoms, the M+1 height ≈ N × 1.1% of the M peak height.

Chemistry

Chemistry · L5 · Advanced Mass Spectrometry

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What is a quantum dot?1 / 12

A semiconductor nanoparticle, typically only a few nanometers across, small enough that quantum confinement effects dominate its electronic behavior — unlike a bulk crystal of the same material, where those effects are negligible.

Chemistry

Chemistry · L5 · Nanomaterials and Quantum Confinement

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