Year 12 Chemistry – Modules 5-8 Key Vocabulary

This set of vocabulary flashcards covers fundamental terms, principles, reactions, analytical techniques, and industrial processes drawn from Modules 5–8 of the Year 12 Chemistry notes. Use them to reinforce key definitions and concepts essential for exam success.

Static equilibrium

A chemical state where forward and reverse reactions have stopped and no molecular changes occur.

Dynamic equilibrium

A state in a closed system where forward and reverse reactions occur simultaneously at equal rates.

Closed system

A reaction vessel in which reactants and products cannot escape; required for chemical equilibrium.

Reversible reaction

A chemical reaction that can proceed in both forward and reverse directions.

Le Chatelier’s principle

If a change is imposed on an equilibrium system, the system shifts to counteract the change and establish a new equilibrium.

Equilibrium position

The relative concentrations of reactants and products at equilibrium.

Equilibrium constant (Keq)

A numerical value expressing the ratio of product to reactant concentrations at equilibrium, each raised to the power of their coefficients.

Solubility product constant (Ksp)

The equilibrium constant for the dissolution of a sparingly soluble ionic compound.

Ionic product (IP)

The product of ion concentrations in solution; compared with Ksp to predict precipitation.

Degree of dissociation

Percentage of a weak acid or base that ionises in solution.

Hydrolysis of salts

Reaction of dissolved ions with water to form acidic or basic solutions.

Amphiprotic species

A substance that can act as both a Brønsted–Lowry acid and base (e.g. HPO4²⁻, H₂O).

pH

Negative logarithm of hydronium ion concentration: pH = −log₁₀[H₃O⁺].

pOH

Negative logarithm of hydroxide ion concentration: pOH = −log₁₀[OH⁻].

Kw

Ion-product constant of water, Kw = 1.0 × 10⁻¹⁴ = [H⁺][OH⁻] at 25 °C.

Conjugate acid–base pair

Two species that differ by a single proton, e.g. NH₄⁺/NH₃.

Buffer solution

A mixture of a weak acid and its conjugate base (or vice versa) that resists pH change upon addition of small amounts of acid or base.

Acid dissociation constant (Ka)

Equilibrium constant for dissociation of a weak acid; smaller Ka indicates a weaker acid.

pKa

Negative logarithm of Ka; larger pKa corresponds to weaker acid strength.

Primary standard

A pure, stable compound (e.g. anhydrous Na₂CO₃) used to prepare a solution of accurately known concentration.

Titration

Volumetric analysis technique where a solution of known concentration reacts with a solution of unknown concentration to determine the latter.

Titre

Volume of titrant delivered from a burette to reach the end point in a titration.

Indicator

A weak acid/base dye that changes colour over a narrow pH range, signalling an end point.

Enthalpy of neutralisation

Heat change when an acid and base react to form water; typically about −57 kJ mol⁻¹ for strong acid–strong base.

Bronsted–Lowry acid

Species that donates a proton (H⁺).

Bronsted–Lowry base

Species that accepts a proton (H⁺).

Lewis acid

Electron-pair acceptor.

Lewis base

Electron-pair donor.

Strong acid

An acid that fully dissociates in water (e.g. HCl).

Weak acid

An acid that partially dissociates in water (e.g. CH₃COOH).

Neutralisation

Reaction between an acid and a base producing water and a salt.

Solubility rules

Empirical guidelines predicting whether ionic compounds are soluble or insoluble in water.

Chromate/dichromate equilibrium

2 CrO₄²⁻ + 2 H⁺ ⇌ Cr₂O₇²⁻ + H₂O, colour change yellow ↔ orange used to illustrate Le Chatelier.

Nitrogen dioxide dimerisation

2 NO₂ ⇌ N₂O₄, equilibrium sensitive to temperature; exothermic forward reaction.

Combustion (non-equilibrium)

Exothermic oxidation of a fuel in an open system where products escape, preventing equilibrium.

Photosynthesis

Endothermic, non-spontaneous conversion of CO₂ and H₂O to glucose and O₂ using solar energy.

Addition reaction

Reaction where atoms add across a double/triple bond of unsaturated hydrocarbons.

Substitution reaction

Reaction where an atom or group in a molecule is replaced by another atom or group (e.g. halogenation of alkanes).

Alkanes

Saturated hydrocarbons with general formula CₙH₂ₙ₊₂; named with suffix −ane.

Alkenes

Unsaturated hydrocarbons containing C=C double bonds; general formula CₙH₂ₙ; suffix −ene.

Alkynes

Unsaturated hydrocarbons containing C≡C triple bonds; general formula CₙH₂ₙ₋₂; suffix −yne.

Alcohols (alkanols)

Organic compounds with hydroxyl (–OH) functional group; named with suffix −ol.

Primary alcohol

Alcohol where the carbon bearing –OH is attached to one other carbon (RCH₂OH).

Secondary alcohol

Alcohol where the –OH carbon is attached to two other carbons (R₁R₂CHOH).

Tertiary alcohol

Alcohol where the –OH carbon is attached to three other carbons (R₁R₂R₃COH).

Carboxylic acid

Organic acid containing the carboxyl (–COOH) group; named with suffix −oic acid.

Ester

Organic compound with functional group –COO– formed from acid + alcohol; named as alkyl alkanoate.

Aldehyde (alkanals)

Organic compound with terminal carbonyl group (–CHO); suffix −al.

Ketone (alkanones)

Organic compound with internal carbonyl group (C=O); suffix −one.

Amine

Organic compound containing amino group (–NH₂); weak base; suffix −amine.

Amide

Derivative of carboxylic acids where –OH is replaced by –NH₂; suffix −amide.

Halogenated hydrocarbon

Hydrocarbon in which one or more hydrogens are replaced by halogen atoms (F, Cl, Br, I).

Isomer

Compounds with same molecular formula but different structural arrangements.

Chain isomer

Isomers differing in branching of the carbon skeleton.

Position isomer

Isomers differing in location of a functional group or substituent.

Functional-group isomer

Isomers containing different functional groups despite same formula.

Dispersion forces

Weak intermolecular attractions arising from temporary dipoles in molecules; dominant in hydrocarbons.

Hydrogen bonding

Strong dipole-dipole interaction between H attached to N,O,F and a lone pair on N,O,F in another molecule.

Fermentation

Anaerobic conversion of sugars (e.g., glucose) to ethanol and CO₂ by yeast at ~37 °C.

Biofuel

Fuel derived from recent biological material (e.g., ethanol, biodiesel).

Soap

Sodium or potassium salt of a fatty acid that forms micelles and acts as a cleaning agent.

Micelle

Spherical aggregate of surfactant molecules with hydrophobic tails inward and hydrophilic heads outward, dispersing oils in water.

Detergent

Synthetic surfactant with long hydrocarbon tail and ionic or polar head; includes anionic, cationic, and non-ionic types.

LDPE (low-density polyethylene)

Highly branched polyethylene produced via free-radical polymerisation; soft, flexible plastic for bags and films.

Polystyrene (PS)

Rigid addition polymer of styrene; used in clear plastics, CD cases, and foam insulation.

PVC (polyvinyl chloride)

Addition polymer of chloroethylene; rigid material for pipes and profiles.

PTFE (polytetrafluoroethylene)

Addition polymer of tetrafluoroethylene; non-stick coating (Teflon).

Condensation polymerisation

Polymer formation via reaction of monomers with elimination of a small molecule (e.g., water).

Polyester (PET)

Condensation polymer formed from ethylene glycol and terephthalic acid; used for fibres and bottles.

Polylactic acid (PLA)

Biodegradable condensation polymer from lactic acid; used in compostable plastics and medical implants.

Colourimetry

Instrumental technique measuring absorbance of visible light to determine concentration of coloured species.

Beer–Lambert law

Relationship A = εcl showing absorbance proportional to concentration and path length.

UV-visible spectrophotometry

Technique measuring absorption of UV or visible light (190–700 nm) to analyse compounds.

λmax

Wavelength at which a substance shows maximum absorbance.

Atomic absorption spectroscopy (AAS)

Technique using light absorption by ground-state atoms to quantify metal ion concentrations.

Flame test

Qualitative test where metal ions emit characteristic colours when heated in a flame.

Gravimetric analysis

Quantitative method where an analyte is precipitated, isolated, dried, and weighed to determine composition.

Precipitation titration

Volumetric analysis based on formation of an insoluble precipitate (e.g., Ag⁺ with Cl⁻, Br⁻, I⁻).

Functional-group test (bromine water)

Rapid decolourisation indicates presence of C=C or C≡C bonds (unsaturation).

Carbon-13 NMR

Spectroscopic method that reveals different carbon environments via chemical shifts (ppm).

Proton NMR

NMR technique that identifies distinct hydrogen environments in organic molecules.

Mass spectrometry

Analytical method that ionises compounds and separates ions by mass-to-charge ratio to identify molecular mass and fragments.

Infrared spectroscopy (IR)

Technique where molecular bonds absorb IR radiation at characteristic frequencies, revealing functional groups.

Haber process

Industrial synthesis of ammonia from N₂ and H₂ at high pressure, moderate temperature, and Fe catalyst.

Solvay process

Industrial method for producing Na₂CO₃ from NaCl, limestone, and NH₃ with CO₂ recycling.

Contact process

Industrial production of H₂SO₄ via catalytic oxidation of SO₂ to SO₃ and absorption in H₂SO₄.

Aspirin (acetylsalicylic acid)

Pharmaceutical synthesized from salicylic acid and acetic anhydride; analgesic and anticoagulant.

Biodiesel

Mixture of long-chain fatty acid esters produced from fats/oils and alcohol (transesterification) used as diesel substitute.

Cation analysis

Qualitative procedures (precipitation, flame colour) to identify metal ions in solution.

Anion analysis

Tests (e.g., AgNO₃ precipitations, acid reactions) used to identify non-metal ions in solution.

Environmental monitoring

Systematic sampling of air, water, soil, and organisms to assess environmental quality.

Surfactant

Surface-active agent with hydrophobic tail and hydrophilic head; lowers surface tension.

Endothermic reaction

Reaction absorbing heat (ΔH > 0).

Exothermic reaction

Reaction releasing heat (ΔH < 0).

Gibbs free energy (ΔG)

Thermodynamic quantity determining spontaneity; negative ΔG indicates spontaneous process.

Activation energy

Minimum energy required for reactants to form products in a chemical reaction.

Collision theory

Model stating that reaction rate depends on frequency and energy of collisions between reactant particles.