STPM Chemistry 962 flashcards
STPM Chemistry 962 · 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.
- Relative atomic mass
- Weighted mean mass of an atom of an element relative to 1/12 the mass of a carbon-12 atom. Calculated from isotopic abundances.
- First ionisation energy
- Energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Aufbau principle
- Electrons occupy the lowest-energy orbitals first, following the order 1s 2s 2p 3s 3p 4s 3d, before higher-energy orbitals are used.
- Hund's rule
- Within a subshell, electrons singly occupy degenerate orbitals with parallel spins before pairing begins, minimising electron repulsion.
- Hydrogen bonding
- A strong intermolecular attraction between a hydrogen atom bonded to N, O or F and a lone pair on a nearby electronegative atom.
- VSEPR theory
- Electron pairs around a central atom arrange to minimise repulsion; lone pairs repel more than bonding pairs, reducing bond angles.
- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound, found from percentage or mass composition.
- Limiting reagent
- The reactant that is completely consumed first in a reaction, determined by dividing moles by the stoichiometric coefficient.
- Ideal gas equation
- pV = nRT, where R is 8.31 J K⁻¹ mol⁻¹ and T is in kelvin. Relates pressure, volume, moles and temperature.
- Graham's law
- The rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass at constant temperature.
- Hess's law
- The enthalpy change of a reaction is independent of the route taken, allowing calculation by summing enthalpy changes of individual steps.
- Standard enthalpy of formation
- Enthalpy change when one mole of a compound forms from its elements in their standard states under standard conditions.
- Le Chatelier's principle
- When a system at equilibrium is disturbed, the position of equilibrium shifts to oppose the change and restore equilibrium.
- Equilibrium constant Kc
- Ratio of product concentrations raised to their coefficients to reactant concentrations raised to theirs, at equilibrium and constant temperature.
- pH definition
- pH = −log₁₀[H⁺]. A decrease of one pH unit corresponds to a tenfold increase in hydrogen ion concentration.
- Buffer solution
- A solution of a weak acid and its conjugate base that resists pH change on adding small amounts of acid or base.
- Rate-determining step
- The slowest elementary step in a reaction mechanism, which controls the overall rate and determines the rate law.
- Activation energy
- The minimum energy colliding particles must possess for a reaction to occur; catalysts lower this value.
- Standard electrode potential
- The potential of a half-cell measured against the standard hydrogen electrode under standard conditions (1 mol dm⁻³, 1 atm, 298 K).
- Oxidation number
- A number assigned to an atom reflecting its electron loss or gain; increases on oxidation and decreases on reduction.
- Markovnikov's rule
- In addition of HX to an unsymmetrical alkene, the hydrogen adds to the carbon bearing more hydrogen atoms.
- Nucleophilic substitution
- A reaction in which a nucleophile replaces a leaving group on a carbon atom, typically in haloalkanes with OH⁻, CN⁻ or NH₃.
- Retention time
- The time a component takes to pass through a chromatography column; used to identify substances by comparison with standards.
- Infrared spectroscopy
- Technique identifying functional groups by absorption of infrared radiation at characteristic wavenumbers, such as C=O near 1700 cm⁻¹.
- Rf value
- In chromatography, the distance travelled by the solute divided by the distance travelled by the solvent front; used for identification.
- Significant figures
- The number of meaningful digits in a measurement, reflecting the precision of the instrument and used when reporting final results.
- Risk assessment
- Identification of hazards in an experiment and the precautions taken to control them, such as fume hoods, goggles and gloves.
- Calibration curve
- A graph of instrument response against known standard concentrations, used to determine the concentration of an unknown sample.
- Mole concept
- One mole contains 6.02 × 10²³ particles; n = m/M relates mass and molar mass for stoichiometric calculations.
- Entropy change
- A measure of disorder; ΔS is positive when a system becomes more disordered, such as solid to gas or fewer moles of gas.
- Electronegativity
- The tendency of an atom to attract the shared pair of electrons in a covalent bond; increases across a period and decreases down a group.
- Solubility product Ksp
- The product of the concentrations of ions in a saturated solution, each raised to its coefficient in the dissolution equation.