OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~480 words · 2 min

Esterification: Alcohol + Acid → Ester + Water You've already met the alcohol group (–OH) and the carboxylic acid group (–COOH). Put an alcohol and a carboxylic acid together — usually with an acid catalyst such as concentrated sulfuric aci

Chemistry

Chemistry · L3 · Esters — Formation and Uses

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Note~775 words · 4 min

What Is Electronegativity? Electronegativity is a measure of how strongly an atom pulls the pair of electrons it shares in a covalent bond toward itself. Every bonded atom has some pull on the shared pair — electronegativity just says how s

Chemistry

Chemistry · L3 · Electronegativity and Bond Polarity

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Note~628 words · 3 min

Catalysts in industry: a gallery beyond Haber and Contact You've already seen iron and vanadium(V) oxide as industrial catalysts — iron in the Haber process, vanadium(V) oxide in the Contact process. A catalyst still means the same thing ev

Chemistry

Chemistry · L3 · Catalysts in Industry

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Note~595 words · 3 min

Common Polyatomic Ions and Their Charges A polyatomic ion is a small group of atoms bonded together that carries one overall charge and behaves as a single unit when building a formula — it gets crossed, subscripted, and bracketed exactly l

Chemistry

Chemistry · L3 · Naming and Writing Ionic Formulae

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Note~586 words · 3 min

Retention Factor: Putting a Number on Chromatography Earlier you saw that dyes spread out on wet paper because they travel at different speeds — some further, some barely at all. The retention factor, Rf, turns that qualitative spreading in

Chemistry

Chemistry · L3 · Chromatography and Rf Values

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Note~813 words · 4 min

Combustion Analysis: Measuring a Formula by Burning It You already know how to write a balanced complete-combustion equation for a hydrocarbon given its formula, and how to turn a GIVEN percent composition into an empirical formula. Combust

Chemistry

Chemistry · L3 · Combustion Analysis

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Note~823 words · 4 min

Specific latent heat: the energy behind a phase change q = mcΔT measures heat that changes a substance's temperature within one state — heating liquid water from 20 °C to 80 °C, for example. But when a substance actually changes state — mel

Chemistry

Chemistry · L3 · Specific Latent Heat

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Note~437 words · 2 min

A titration that isn't about pH at all An acid–base titration tracks proton transfer, and its endpoint is flagged by a pH indicator. A REDOX titration swaps both of those out: the titrant and analyte react by transferring electrons, not pro

Chemistry

Chemistry · L3 · Redox Titrations

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Note~492 words · 2 min

Organic reaction mechanisms: nucleophiles, electrophiles, and arrow pushing A reaction mechanism is a step-by-step account of how bonds break and form during a chemical reaction. Each elementary step is represented by curved arrows that sho

Chemistry

Chemistry · L4 · Organic reaction mechanisms: nucleophiles, electrophiles, and arrow pushing

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Note~431 words · 2 min

Acid–base equilibria: pH, buffers, and Ka Acid–base chemistry governs a vast range of biological, industrial, and environmental processes. Two complementary definitions frame the subject: Brønsted–Lowry (proton transfer) and Lewis (electron

Chemistry

Chemistry · L4 · Acid–base equilibria: pH, buffers, and Ka

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Note~396 words · 2 min

Thermochemistry: enthalpy, entropy, and free energy Thermochemistry investigates the heat changes that accompany chemical reactions. The three central quantities — enthalpy (H), entropy (S), and Gibbs free energy (G) — together determine wh

Chemistry

Chemistry · L4 · Thermochemistry: enthalpy, entropy, and free energy

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Note~411 words · 2 min

Chemical kinetics: rate laws, activation energy, and catalysis Chemical kinetics studies how fast reactions occur and what factors govern reaction rate. Kinetics is distinct from thermodynamics: a reaction can be thermodynamically spontaneo

Chemistry

Chemistry · L4 · Chemical kinetics: rate laws, activation energy, and catalysis

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Note~698 words · 3 min

Electrochemistry: standard potentials, the Nernst equation, and cell types The earlier introduction to redox covered the qualitative picture: OIL RIG, spotting which species is oxidised and which is reduced, and how a galvanic cell wires th

Chemistry

Chemistry · L4 · Electrochemistry: standard potentials, the Nernst equation, and cell types

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Note~539 words · 3 min

Coordination complexes: ligands, naming, and why they're colored A coordination complex has a central transition metal ion surrounded by ligands — molecules or ions that each donate a lone electron pair to the metal, forming a coordinate (d

Chemistry

Chemistry · L4 · Coordination complexes: ligands, naming, and why they're colored

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Note~753 words · 4 min

Colligative Properties (Quantitative) The L3 treatment of colligative properties is purely qualitative: dissolved particles 'get in the way' of the solvent, so freezing point drops, boiling point rises, and evaporation slows. That intuition

Chemistry

Chemistry · L4 · Colligative Properties (Quantitative)

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Note~683 words · 3 min

Solubility equilibria: Ksp, the common ion effect, and precipitation Many ionic compounds are only sparingly soluble in water: a small amount dissolves, and the rest remains as undissolved solid in equilibrium with its dissolved ions. This

Chemistry

Chemistry · L4 · Solubility Equilibria: Ksp, common ion effect, and precipitation

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Note~892 words · 4 min

Intermolecular forces & molecular polarity — vectors, polarizability, and boiling-point trends London dispersion, dipole-dipole, and hydrogen bonding explain WHICH forces act between molecules. This note goes one step further and asks HOW S

Chemistry

Chemistry · L4 · Intermolecular forces & molecular polarity — vectors, polarizability, and boiling-point trends

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Note~594 words · 3 min

The oxidation ladder: alcohols → aldehydes/ketones → carboxylic acids Alcohols, aldehydes, ketones, and carboxylic acids are all connected by a single idea: oxidation state at carbon. Climbing the ladder from alcohol to acid means removing

Chemistry

Chemistry · L4 · The oxidation ladder: alcohols → aldehydes/ketones → carboxylic acids

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Note~700 words · 4 min

Aromatic Chemistry & Electrophilic Aromatic Substitution Benzene looks, on paper, like it should behave as three alkenes stitched into a ring — reactive C=C bonds ready to add bromine or hydrogen the way any alkene would. It doesn't. Benzen

Chemistry

Chemistry · L4 · Aromatic Chemistry & Electrophilic Aromatic Substitution

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Note~846 words · 4 min

Stereochemistry: Chirality, Enantiomers, and R/S Naming Two molecules can share exactly the same atoms, connected in exactly the same order, and still be different compounds — differing only in how their atoms are arranged in three-dimensio

Chemistry

Chemistry · L4 · Stereochemistry: Chirality, Enantiomers, and R/S Naming

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Note~1157 words · 6 min

Nuclear Chemistry: The Decay Law, Mass Defect & Binding Energy At L3 you saw radioactive decay as a halving staircase — after each half-life, whatever is left gets cut in half again. That picture is correct but incomplete: it only gives cle

Chemistry

Chemistry · L4 · Nuclear Chemistry: The Decay Law, Mass Defect & Binding Energy

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Note~996 words · 5 min

Solid state chemistry: crystal classes and unit cells Most solids we handle are crystalline: their particles pack into an ordered, repeating three-dimensional pattern rather than sitting in random disorder. What holds a particular solid tog

Chemistry

Chemistry · L4 · Solid state chemistry: crystal classes and unit cells

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Note~548 words · 3 min

Spectroscopy basics: what each technique measures Spectroscopy is a family of techniques built on one idea: shine a form of energy at a sample and see what happens to it. What gets absorbed, transmitted, or emitted depends on the sample's s

Chemistry

Chemistry · L4 · Spectroscopy basics: what each technique measures

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Note~855 words · 4 min

Gibbs free energy: the four cases, the crossover point, and the road to K This note assumes you already have ΔG = ΔH − TΔS and the idea that ΔG < 0 means spontaneous. Here we go further: work through the reasoning behind all four ΔH/ΔS sign

Chemistry

Chemistry · L4 · Gibbs free energy: the four cases, the crossover point, and the road to K

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Note~1002 words · 5 min

Classifying polymers by thermal and mechanical behavior L3 covered HOW polymer chains get built — addition versus condensation. This note asks a different question: once a chain exists, how does the material actually BEHAVE when you heat it

Chemistry

Chemistry · L4 · Classifying Polymers by Thermal & Mechanical Behavior

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Note~680 words · 3 min

From amino acids to protein structure — a chemist's view A protein is, chemically, a long chain built from a small alphabet of monomers — the 20 standard amino acids — joined end to end by a single repeating bond type. Understanding a prote

Chemistry

Chemistry · L4 · From amino acids to protein structure — a chemist's view

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Note~627 words · 3 min

Real Gases & the Ideal Gas Law Boyle's law, Charles's law, and Avogadro's law each describe how two of a gas's variables relate while the others are held fixed. Combine all three and you get one master equation that handles any two states o

Chemistry

Chemistry · L4 · Real Gases & the Ideal Gas Law

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Note~741 words · 4 min

Catalysis and green chemistry: lowering barriers, cutting waste A catalyst speeds up a reaction by opening an alternate pathway with a lower activation energy (Ea), without being consumed overall — it may take part in an intermediate step,

Chemistry

Chemistry · L4 · Catalysis and green chemistry: lowering barriers, cutting waste

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Note~647 words · 3 min

Transition metal chemistry in solution: colors, amphoterism, and trends Beyond the coordination chemistry of ligands and geometry, transition metals show a set of characteristic descriptive behaviors in aqueous solution: distinctive aqua-io

Chemistry

Chemistry · L4 · Transition metal chemistry in solution: colors, amphoterism, and trends

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Note~957 words · 5 min

Polyprotic acids: stepwise dissociation, successive Ka values, and multi-equivalence-point titrations A polyprotic acid loses more than one proton, but it does so one proton at a time, through a series of distinct equilibria — each with its

Chemistry

Chemistry · L4 · Polyprotic acids: stepwise dissociation, successive Ka values, and multi-equivalence-point titrations

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