OpenStem

@openstem · Joined Jul 2026

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Flashcards6 cards

What is a unit cell?1 / 6

The smallest repeating three-dimensional block of a crystal lattice that, when tiled in all three directions with no gaps or overlaps, reproduces the entire crystal structure.

Chemistry

Chemistry · L4 · Solid State Chemistry — Unit Cells & Cubic Packing

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Flashcards10 cards

What is the general idea behind spectroscopy?1 / 10

Shine a form of energy (usually light) at a sample and see what happens to it — what gets absorbed, transmitted, or emitted. Because different structures interact with energy differently, the result reveals something about the sample's structure.

Chemistry

Chemistry · L4 · Spectroscopy Basics

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Flashcards9 cards

What determines whether a reaction is spontaneous, and why does temperature only matter for two of the four ΔH/ΔS sign combinations?1 / 9

The sign of ΔG = ΔH − TΔS. When ΔH and −TΔS push in the SAME direction for every T (both negative, or both positive), the sign of ΔG never changes — spontaneity is fixed, regardless of temperature. When they push in OPPOSITE directions, the two terms compete, and which one wins depends on how large T is — so spontaneity can flip at some crossover temperature.

Chemistry

Chemistry · L4 · Gibbs Free Energy — Spontaneity Cases & Crossover Temperature

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Flashcards6 cards

What equation connects the standard free energy change ΔG° to the equilibrium constant K?1 / 6

— where R = 8.314 J mol⁻¹ K⁻¹ and T is in kelvin. This is the bridge between thermodynamics (ΔG°, a single measured or calculated number) and equilibrium (K, the ratio of product to reactant activities at equilibrium).

Chemistry

Chemistry · L4 · Gibbs Free Energy — ΔG° and the Equilibrium Constant K

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Flashcards7 cards

What structural feature distinguishes a thermoplastic from a thermoset?1 / 7

Cross-linking. A thermoplastic's chains are NOT chemically bonded to each other — they're just long, tangled, individual strands held together by weaker intermolecular forces. A thermoset's chains ARE cross-linked: covalent bonds welded between chains during curing lock the whole mass into one giant molecular network.

Chemistry

Chemistry · L4 · Thermoplastics, Thermosets & Elastomers

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Why can't a polymer sample be assigned a single, exact molecular weight the way a small molecule like glucose can?1 / 6

A polymerization reaction doesn't stop every chain at exactly the same length — some chains stop growing early, some keep adding monomers longer, purely by chance during the reaction. A single batch of polymer is really a mixture of chains of many different lengths, so 'molecular weight' has to describe that whole distribution, not one exact value.

Chemistry

Chemistry · L4 · Polymer Molecular Weight & Polydispersity

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Draw out (in words) the four groups bonded to the central alpha carbon of a generic amino acid.1 / 7

An amino group (–NH₂), a carboxylic acid group (–COOH), a hydrogen atom, and a variable side chain called the R group. All four attach to the same central carbon, the alpha carbon. This four-substituent skeleton is identical across all 20 standard amino acids — only the R group changes.

Chemistry

Chemistry · L4 · Amino Acid Structure

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Flashcards11 cards

What is the ideal gas law, and what does each symbol represent?1 / 11

P = pressure (atm), V = volume (L), n = amount of gas (mol), T = absolute temperature (K), R = the gas constant. It combines Boyle's law (P ∝ 1/V), Charles's law (V ∝ T), and Avogadro's law (V ∝ n) into one relationship — each of those laws is just PV = nRT with two of the four variables held fixed.

Chemistry

Chemistry · L4 · Real Gases & the Ideal Gas Law

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Flashcards12 cards

What does a catalyst do to a reaction, in terms of activation energy and its own fate?1 / 12

A catalyst provides an alternate reaction pathway with a lower activation energy (Ea), so more reactant molecules have enough energy to react at a given temperature. It is regenerated at the end of the mechanism — not consumed overall — even though it may take part in an intermediate step.

Chemistry

Chemistry · L4 · Catalysis & Green Chemistry

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What color is a dilute aqueous solution of Cu²⁺ (e.g. CuSO₄(aq))?1 / 12

Pale blue. The hydrated copper(II) ion, [Cu(H₂O)₆]²⁺, gives copper sulfate solutions and crystals their familiar blue color — one of the most recognisable transition-metal aqua-ion colors in the lab.

Chemistry

Chemistry · L4 · Transition Metal Chemistry in Solution

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What is a polyprotic acid, and what are the three ionisation steps of phosphoric acid, H₃PO₄?1 / 11

A polyprotic acid can donate more than one proton per molecule, but only one at a time. H₃PO₄ ionises in three steps: H₃PO₄ ⇌ H⁺ + H₂PO₄⁻ (Ka1), H₂PO₄⁻ ⇌ H⁺ + HPO₄²⁻ (Ka2), HPO₄²⁻ ⇌ H⁺ + PO₄³⁻ (Ka3). Each step removes a proton from the species produced by the previous step, not from the original acid directly.

Chemistry

Chemistry · L4 · Polyprotic Acids

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Write the three integrated rate laws for zero-, first-, and second-order reactions, and state the units of k for each.1 / 10

Zero order: [A] = [A]₀ − kt (k in mol L⁻¹ s⁻¹). First order: ln[A] = ln[A]₀ − kt (k in s⁻¹). Second order: 1/[A] = 1/[A]₀ + kt (k in L mol⁻¹ s⁻¹). Each is a straight-line equation in a different pair of variables — that's exactly what the linearization method exploits.

Chemistry

Chemistry · L4 · Integrated Rate Laws

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What is the Chapman cycle?1 / 12

The four-reaction cycle of UV photolysis and recombination that continuously forms and destroys ozone (O₃) in the stratosphere, maintaining a roughly steady-state ozone concentration long before any human influence existed.

Chemistry

Chemistry · L4 · Atmospheric Chemistry — Ozone and the Greenhouse Effect

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How does the Lewis definition of an acid differ from the Brønsted-Lowry definition?1 / 10

Brønsted-Lowry: an acid donates a proton (H⁺). Lewis: an acid accepts a pair of electrons — a broader definition that includes species with no protons at all, such as BF₃ or a bare metal cation.

Chemistry

Chemistry · L4 · Lewis Acids and Bases

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What happens in the first step of electrophilic addition of HX to an alkene?1 / 11

The alkene's π electrons act as the nucleophile and attack the electrophilic H of H–X, forming a new C–H bond. This leaves a positive charge (a carbocation) on the OTHER alkene carbon, while X⁻ is released as a spectator ion. This protonation step is rate-determining.

Chemistry

Chemistry · L4 · Addition and Elimination Mechanisms

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Starting from the Ka expression for a weak acid HA, derive the Henderson–Hasselbalch equation.1 / 10

Ka = [H⁺][A⁻]/[HA]. Taking −log of both sides: −log Ka = −log[H⁺] − log([A⁻]/[HA]), i.e. pKa = pH − log([A⁻]/[HA]). Rearranging gives

Chemistry

Chemistry · L4 · Buffer Calculations and Capacity

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What is a formation constant (Kf), also called a stability constant, for a complex ion?1 / 11

Kf is the equilibrium constant for a free (hydrated) metal ion combining with ligands to form a complex ion, e.g. Mⁿ⁺(aq) + xL(aq) ⇌ [MLₓ]ⁿ⁺(aq), Kf = [MLₓⁿ⁺] / ([Mⁿ⁺][L]ˣ). Formation constants are often very large (10⁶ to 10³⁵ or more), meaning that once enough ligand is present, essentially all the free metal ion converts into the complex.

Chemistry

Chemistry · L4 · Complex Ions and Solubility

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State Hess's Law, and explain WHY it works in terms of a fundamental property of enthalpy.1 / 10

Hess's Law: if a reaction can be written as the sum of two or more steps, its overall ΔH equals the sum of the ΔH values of those steps, however the steps are combined. It works because enthalpy is a STATE FUNCTION — ΔH depends only on the initial and final states of a system, not on the path taken between them. Any route from the same reactants to the same products, no matter how many intermediate steps, must add up to the same total ΔH.

Chemistry

Chemistry · L4 · Hess's Law Calculations

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What do the single line "|" and double line "||" mean in cell notation?1 / 10

A single vertical line "|" marks a phase boundary — for example between a solid electrode and its surrounding aqueous solution. A double vertical line "||" marks the salt bridge (or porous membrane) separating the two half-cells. Everything to the left of "||" is one half-cell; everything to the right is the other.

Chemistry

Chemistry · L4 · Cell Notation and Concentration Cells

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What is a back titration (indirect titration), and why use one instead of titrating the analyte directly?1 / 10

A back titration adds a KNOWN, precisely measured EXCESS of a standard reagent to the sample — enough to react completely with the analyte — then titrates the LEFTOVER (unreacted) excess with a second standard solution. It's used when the analyte can't be titrated directly: e.g. it's an insoluble solid, it reacts too slowly with a titrant to give a stable endpoint, or no indicator gives a sharp colour change for the direct reaction.

Chemistry

Chemistry · L4 · Back Titration

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What is a 'diagonal relationship' in the periodic table, and where does the best-known example sit?1 / 11

A diagonal relationship is when an element resembles the element one period down and one group to the right more than it resembles other members of its own group. The classic trio sits at the top-left of the table: lithium resembles magnesium, beryllium resembles aluminium, and boron resembles silicon.

Chemistry

Chemistry · L4 · Periodic Anomalies

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You add NaOH dropwise to a colourless unknown cation solution and get a white precipitate. What single further test narrows down which white-precipitate cation you have?1 / 11

Add excess NaOH to a fresh portion of the sample. If the white precipitate redissolves to a colourless solution, the cation is amphoteric (Al³⁺, Zn²⁺, or Pb²⁺); if the precipitate is unchanged, it is a different, non-amphoteric white-hydroxide cation.

Chemistry

Chemistry · L4 · Systematic Qualitative Inorganic Analysis

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Flashcards12 cards

What is a reaction intermediate, and why can't its concentration be handled with simple algebra the way a stable reactant can?1 / 12

An intermediate is a species produced by one elementary step and consumed by a later one — it never appears in the overall equation. Because it is typically short-lived and reactive, we can't just measure its concentration directly; we need an approximation to eliminate it from the rate law.

Chemistry

Chemistry · L4 · The Steady-State Approximation

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State Faraday's first law of electrolysis in words.1 / 11

The mass of a substance produced (or dissolved) at an electrode during electrolysis is directly proportional to the quantity of electric charge, Q, passed through the cell. Double the charge, double the mass deposited.

Chemistry

Chemistry · L4 · Faraday's Laws of Electrolysis

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How does instrumental chromatography (HPLC, GC) differ fundamentally from paper or TLC chromatography?1 / 12

There is no visible spot on a stationary surface to measure by eye. Instead, the mobile phase carries the sample through an enclosed column, a detector at the far end registers each compound as it emerges, and the compound is characterized by how long it took to travel through the column — its retention time — rather than by a distance travelled up a plate.

Chemistry

Chemistry · L4 · Instrumental Chromatography — HPLC and GC

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What raw materials go into a blast furnace, and what is each one for?1 / 12

Four raw materials are charged into the top of the furnace: iron ore (hematite, Fe₂O₃) — the source of iron; coke (carbon) — burned as fuel and used as the reducing agent; limestone (calcium carbonate) — added as a flux to remove impurities; and a blast of hot air blown in near the base, which burns the coke and drives the whole process.

Chemistry

Chemistry · L4 · Blast Furnace and Electrolytic Refining

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What is EDTA, and why is it described as a hexadentate ligand?1 / 10

EDTA (ethylenediaminetetraacetic acid) is a chelating ligand with six donor atoms — two nitrogen atoms (from its two amine groups) and four oxygen atoms (from its four carboxylate groups) — all of which can coordinate to a single metal ion at the same time. Because it offers six donor atoms simultaneously, EDTA is hexadentate: it wraps around a metal ion almost completely, like a claw, rather than approaching from just one side.

Chemistry

Chemistry · L4 · EDTA Complexometric Titration

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Describe the shape of a strong-acid/strong-base titration curve, and state the pH at the equivalence point.1 / 10

The curve starts at a low pH, rises gradually, then shows a very steep, near-vertical jump through the equivalence point, before leveling off at high pH. Because the reaction produces only a neutral salt (e.g. NaCl from HCl + NaOH — neither ion hydrolyses), the equivalence point sits at exactly pH = 7.00 at 25 °C.

Chemistry

Chemistry · L4 · Acid-Base Titration Curves & Indicator Selection

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Flashcards9 cards

Define lattice energy precisely, including the direction of the process and the sign convention used here.1 / 9

Lattice energy (ΔH_lattice) is the enthalpy change when one mole of an ionic solid forms from its gaseous ions: M⁺(g) + X⁻(g) → MX(s). This process is always strongly exothermic (electrostatic attraction releases energy as the ions come together), so ΔH_lattice is a large negative number under this formation-direction convention. (Some sources define lattice energy as the reverse, lattice-breaking process, and report it as positive — always check which direction a given value refers to.)

Chemistry

Chemistry · L4 · Lattice Energy: Trends, the Born-Lande Equation, and the Kapustinskii Equation

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Define transmittance (T) and absorbance (A), and give the equation relating them.1 / 10

Transmittance T = I/I₀ is the fraction of incident light intensity (I₀) that passes through the sample and reaches the detector (I) — a value between 0 and 1 (or 0–100% as %T). Absorbance is the base-10 negative logarithm of transmittance:

Chemistry

Chemistry · L4 · Colorimetry & the Beer-Lambert Law

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