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@openstem · Joined Jul 2026

7420 public items8 groups

Note~1099 words · 5 min

Integrated rate laws: concentration, time, half-life, and linearization A single set of concentration-vs-time measurements from one experiment can pin down BOTH the reaction order and the rate constant k — without running a whole series of

Chemistry

Chemistry · L4 · Integrated Rate Laws: concentration-time relationships, half-lives, and linearization

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Note~1028 words · 5 min

Stratospheric ozone chemistry and the greenhouse effect Two of the most consequential pieces of atmospheric chemistry are also two of the most casually explained. 'CFCs destroy the ozone layer' and 'CO₂ traps heat' are both true, but both s

Chemistry

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

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Note~712 words · 4 min

Lewis acids and bases: the electron-pair framework The Brønsted-Lowry theory defines acids and bases by proton transfer, but many important reactions involve no proton at all. The Lewis theory reframes acid-base chemistry in terms of electr

Chemistry

Chemistry · L4 · Lewis Acids and Bases

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Note~1056 words · 5 min

Addition and elimination mechanisms Alkenes and alkyl halides sit at opposite ends of the same reaction: an alkyl halide can be built by ADDING H–X across a double bond, and an alkene can be recovered by ELIMINATING H–X from an alkyl halide

Chemistry

Chemistry · L4 · Addition and Elimination Mechanisms

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Note~1109 words · 6 min

Buffer calculations and capacity A buffer's qualitative behaviour — a weak acid and its conjugate base sharing the work of soaking up added acid or base — only goes so far. To actually predict a buffer's pH, and to know how much stress it c

Chemistry

Chemistry · L4 · Buffer Calculations and Capacity: Henderson–Hasselbalch, worked pH calculations, and capacity

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Note~726 words · 4 min

Complex-ion formation and its effect on solubility A salt with a tiny Ksp can still be made to dissolve almost completely if something in solution reacts with the metal ion as fast as the salt releases it. That 'something' is usually a liga

Chemistry

Chemistry · L4 · Complex Ions and Solubility

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Note~964 words · 5 min

Hess's Law calculations: building an unmeasurable ΔH from measurable steps Enthalpy is a state function: ΔH for a reaction depends only on the initial and final states, not on the path taken between them. Hess's Law turns that fact into a c

Chemistry

Chemistry · L4 · Hess's Law calculations: cycles, scaling, and the Born–Haber cycle

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Note~848 words · 4 min

Cell notation and concentration cells The earlier note on electrochemistry built up E°cell, ΔG° = −nFE°, and the Nernst equation from two half-reactions described in words. This note adds two things on top of that foundation: a compact, sta

Chemistry

Chemistry · L4 · Cell Notation and Concentration Cells

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Note~805 words · 4 min

Back titration: when you can't titrate directly A direct titration works when the analyte is dissolved, reacts quickly and cleanly with the titrant, and gives a sharp, reliable endpoint. A back titration is what you reach for when one of th

Chemistry

Chemistry · L4 · Back Titration: The Excess-and-Subtract Method

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Note~932 words · 5 min

Periodic anomalies: diagonal relationships, lanthanide contraction, and the inert-pair effect The four core trends — atomic radius, ionization energy, electronegativity, metallic character — and the ionization-energy dips at Be→B and N→O ex

Chemistry

Chemistry · L4 · Periodic Anomalies

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Note~680 words · 3 min

Beyond a single test A single spot test — one reagent, one observation — can narrow an unknown down, but several common cations look identical after just one step: more than one gives a white precipitate with sodium hydroxide, for instance.

Chemistry

Chemistry · L4 · Systematic Qualitative Inorganic Analysis

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Note~875 words · 4 min

The steady-state approximation: deriving a rate law from a mechanism A proposed mechanism often contains a reactive intermediate — a species formed by one step and consumed by another, never appearing in the overall equation. Its concentrat

Chemistry

Chemistry · L4 · The Steady-State Approximation

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Note~944 words · 5 min

Faraday's laws of electrolysis: from current and time to mass deposited The earlier qualitative picture of electrolysis established which ion goes to which electrode, and what happens to it there — cations reduced at the cathode, anions oxi

Chemistry

Chemistry · L4 · Faraday's Laws of Electrolysis: quantifying charge, moles of electrons, and mass deposited

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Note~599 words · 3 min

Instrumental Chromatography: HPLC and GC Paper and TLC chromatography separate a mixture across a flat, visible surface: you can see each spot and measure how far it travelled. Instrumental chromatography does the same underlying job — sepa

Chemistry

Chemistry · L4 · Instrumental Chromatography — HPLC and GC

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Note~818 words · 4 min

Blast Furnace and Electrolytic Refining The general rule is already familiar: an unreactive metal like gold is found native, a moderately reactive metal like iron is extracted by reduction with carbon, and a highly reactive metal like alumi

Chemistry

Chemistry · L4 · Blast Furnace and Electrolytic Refining

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Note~872 words · 4 min

EDTA Complexometric Titration Formation constants (Kf) show that a ligand can bind a metal ion strongly enough to pull an otherwise-unfavourable equilibrium along with it. Complexometric titration puts that same chemistry to direct, quantit

Chemistry

Chemistry · L4 · EDTA Complexometric Titration

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Note~922 words · 5 min

Titration curves: shape, the half-equivalence point, and choosing an indicator A titration curve plots pH against volume of titrant added. Its overall shape — where it starts, how gradually it rises, and how sharp the jump at equivalence is

Chemistry

Chemistry · L4 · Titration curve shapes, the half-equivalence point, and indicator selection

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Note~863 words · 4 min

Lattice energy: charge, radius, and two ways to calculate it The Born-Haber cycle (covered as a Hess's-Law application elsewhere) is one way to obtain a lattice energy: measure everything else in the cycle experimentally and solve for the o

Chemistry

Chemistry · L4 · Lattice energy: what controls its size, and two ways to calculate it

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Note~725 words · 4 min

Colorimetry and the Beer-Lambert law Colorimetry determines the concentration of a coloured species by measuring how much light of a chosen wavelength it absorbs. The whole technique rests on one proportionality — the Beer-Lambert law — con

Chemistry

Chemistry · L4 · Colorimetry and the Beer-Lambert law

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Note~623 words · 3 min

Effusion, diffusion, and Graham's law Kinetic molecular theory treats gas molecules as constantly moving particles whose average kinetic energy depends only on temperature — not on what the gas actually is. That single fact, applied to two

Chemistry

Chemistry · L4 · Effusion, diffusion, and Graham's law

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Note~727 words · 4 min

Heterogeneous equilibria: multiple phases, one equilibrium constant Every equilibrium studied so far in aqueous acid-base and solubility chemistry has involved species dissolved in the same solution — a homogeneous equilibrium. Many importa

Chemistry

Chemistry · L4 · Heterogeneous equilibria: omitted phases, Kp, and the Kp–Kc relationship

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Note~725 words · 4 min

Mass spectrometry fragmentation: reading a spectrum's fingerprint A mass spectrum plots the relative abundance of ions against their mass-to-charge ratio (m/z). In electron impact (EI) mass spectrometry, a high-energy electron beam does mor

Chemistry

Chemistry · L4 · Mass spectrometry fragmentation: molecular ions, alpha cleavage, and isotope patterns

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Note~672 words · 3 min

Organic synthesis routes: retrosynthetic analysis and a worked example Planning a multi-step organic synthesis rarely starts by asking 'what does this starting material turn into?' — it starts at the TARGET and works backwards. Retrosynthet

Chemistry

Chemistry · L4 · Retrosynthetic analysis and a worked multi-step synthesis

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Note~713 words · 4 min

Balancing redox equations by half-reactions, and redox titrations A redox equation can't always be balanced by inspection — especially once polyatomic ions like MnO₄⁻ or Cr₂O₇²⁻ are involved. The half-reaction (ion-electron) method balances

Chemistry

Chemistry · L4 · Balancing redox equations by half-reactions, and redox titrations

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Note~626 words · 3 min

Calorimetry calculations: measuring heat directly Hess's Law calculations combine already-known ΔH values algebraically. Calorimetry is how those ΔH values get measured in the first place — by tracking a temperature change in a known mass o

Chemistry

Chemistry · L4 · Calorimetry calculations: q = mcΔT, calorimeter types, and ΔH vs ΔU

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Note~231 words · 1 min

Arrhenius Equation The empirical Arrhenius equation describes how the rate constant k depends on temperature T: where A is the pre-exponential (frequency) factor, Eₐ is the activation energy (J mol⁻¹), R = 8.314 J mol⁻¹ K⁻¹ is the gas const

Chemistry

Chemistry · L5 · Chemical Kinetics: Eyring & Arrhenius Equations

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Note~259 words · 1 min

¹H NMR Chemical Shifts Chemical shift δ (ppm) reflects the local electronic environment relative to TMS (δ = 0). Key reference values: Spin–Spin Coupling: the n + 1 Rule For first-order spectra, a proton coupled to n equivalent neighbouring

Chemistry

Chemistry · L5 · Spectroscopy Interpretation: NMR, IR, and MS

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Note~198 words · 1 min

Secular Determinant from Variational Principle For an MO ψ = Σᵢ cᵢχᵢ, minimising E = ⟨ψ|Ĥ|ψ⟩/⟨ψ|ψ⟩ with respect to each cⱼ yields the secular equations: Non-trivial solutions require the secular determinant to vanish: Hückel Results for Ben

Chemistry

Chemistry · L5 · Molecular Orbital Theory: Secular Equations & Frontier Orbitals

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Note~807 words · 4 min

The Boltzmann Distribution In a system at thermal equilibrium, molecules are distributed over their available energy states according to the Boltzmann distribution: the ratio of populations in two states depends only on their energy gap and

Chemistry

Chemistry · L5 · Statistical Thermodynamics: Boltzmann Distribution, Partition Functions & Entropy

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Note~780 words · 4 min

Ligand field theory: spectrochemical series, spin state, and Jahn–Teller distortion L4 crystal field theory establishes that ligands split a metal's five d-orbitals into two energy levels separated by a gap Δo. Ligand field theory pushes th

Chemistry

Chemistry · L5 · Ligand Field Theory: Spectrochemical Series, Spin State, and Jahn–Teller Distortion

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