KSEAB II PUC Chemistry flashcards
KSEAB II PUC Chemistry · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Avogadro constant
- The number of particles present in one mole of a substance, equal to 6.022×10²³ mol⁻¹. It links the mass of a sample to the number of atoms or molecules it contains.
- Limiting reagent
- The reactant that is completely consumed first in a chemical reaction and therefore determines the maximum amount of product formed. Other reactants remain in excess.
- Empirical formula
- The formula showing the simplest whole-number ratio of atoms of each element in a compound. It is obtained from percentage composition by dividing by the smallest mole ratio.
- Rydberg equation
- 1/λ = R_H Z²(1/n₁² − 1/n₂²) predicts the wavelength of light emitted when an electron falls between hydrogen atom energy levels. R_H equals 1.097×10⁷ m⁻¹.
- Heisenberg uncertainty principle
- It is impossible to determine both the position and momentum of an electron simultaneously with arbitrary precision. The product of the uncertainties is at least h/4π.
- Hund's rule
- Orbitals of equal energy are each occupied by one electron with parallel spins before any orbital receives a second electron, minimising electron repulsion.
- Bond order
- Half the difference between the number of bonding and antibonding electrons in a molecular orbital diagram. Higher bond order corresponds to a shorter and stronger bond.
- VSEPR theory
- Valence shell electron pair repulsion theory predicts molecular shape by arranging electron pairs around the central atom so that repulsions between them are minimised.
- Hydrogen bond
- An attractive force between a hydrogen atom covalently bonded to N, O or F and a lone pair on a nearby electronegative atom, raising boiling points of water and hydrogen fluoride.
- Ideal gas equation
- PV = nRT relates pressure, volume, amount and absolute temperature of an ideal gas. R equals 8.314 J K⁻¹ mol⁻¹ in SI units.
- Hess's law
- The enthalpy change of a reaction is independent of the route taken, so it can be calculated by summing the enthalpy changes of individual steps.
- Gibbs energy criterion
- ΔG = ΔH − TΔS determines spontaneity: a negative ΔG means the process is spontaneous, zero means equilibrium, and positive means non-spontaneous.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, the equilibrium shifts in the direction that counteracts the disturbance.
- Buffer solution
- A solution of a weak acid and its salt, or a weak base and its salt, that resists pH change on adding small amounts of acid or base.
- Oxidising agent
- A species that accepts electrons from another substance and is itself reduced. Its oxidation number decreases during the reaction.
- Colligative properties
- Properties of solutions that depend on the number of solute particles present rather than their nature: vapour pressure lowering, boiling point elevation, freezing point depression and osmotic pressure.
- van't Hoff factor
- The ratio of the observed colligative effect to the calculated value for a non-dissociating solute. It accounts for dissociation or association of solute particles.
- Henry's law
- The partial pressure of a gas above a solution is proportional to its mole fraction in the solution: p = K_H x. Solubility falls as temperature rises.
- Nernst equation
- E = E° − (0.0591/n) log Q at 25 °C gives the cell potential when concentrations are not standard, where Q is the reaction quotient.
- First-order half-life
- For a first-order reaction, t₁/₂ = 0.693/k. The half-life is constant and independent of the initial concentration of the reactant.
- Arrhenius equation
- k = A e^(−E_a/RT) shows that the rate constant increases with temperature and decreases with activation energy. A is the pre-exponential factor.
- Lanthanoid contraction
- The gradual decrease in atomic and ionic radii across the lanthanoid series caused by poor shielding of nuclear charge by 4f electrons.
- Interstitial compounds
- Compounds formed when small atoms such as hydrogen, carbon or nitrogen occupy the spaces between metal atoms in a crystal lattice, making the metal harder.
- Crystal field splitting
- The energy difference Δ_o between the d orbitals of a metal ion in a complex, produced by ligand repulsion. It determines colour and spin state.
- Effective atomic number
- EAN equals the atomic number of the metal minus its oxidation state plus twice the coordination number, estimating the electron count around the central ion.
- SN1 mechanism
- A two-step nucleophilic substitution in which the leaving group departs first to form a carbocation, followed by attack of the nucleophile. Tertiary halides react fastest.
- Lucas test
- A test using concentrated HCl and zinc chloride that distinguishes alcohols: tertiary gives immediate turbidity, secondary on warming, and primary does not react.
- Tollens' reagent
- An ammoniacal silver nitrate solution that is reduced by aldehydes to give a silver mirror, distinguishing aldehydes from ketones.
- Hinsberg test
- A reaction with benzenesulfonyl chloride that distinguishes amines: primary gives a soluble sulfonamide, secondary an insoluble one, and tertiary no reaction.
- Peptide bond
- An amide linkage formed between the carboxyl group of one amino acid and the amino group of another, with the elimination of a water molecule.
- Vulcanisation
- The process of heating natural rubber with sulphur to form cross-links between polymer chains, making the rubber harder, stronger and less sticky.
- Flame test
- A qualitative test in which a metal salt is heated in a flame and identified by its characteristic colour, such as golden yellow for sodium and lilac for potassium.