GCE A/L Chemistry flashcards
GCE A/L 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.
- Atomic number
- The number of protons in the nucleus of an atom; it uniquely identifies the element and determines the number of electrons in a neutral atom.
- Isotopes
- Atoms of the same element with the same number of protons but different numbers of neutrons, hence different mass numbers and sometimes different physical properties.
- Hund's rule
- Electrons occupy degenerate orbitals singly with parallel spins before any pairing occurs, minimising electron–electron repulsion within a subshell.
- First ionisation energy
- The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Electronegativity
- The tendency of an atom in a molecule to attract the shared pair of electrons in a covalent bond towards itself; increases across a period and decreases down a group.
- VSEPR theory
- Valence shell electron pair repulsion theory: electron domains around a central atom arrange themselves as far apart as possible; lone pairs repel more strongly than bonding pairs.
- Hydrogen bonding
- A strong intermolecular force between a hydrogen atom bonded to N, O or F and a lone pair on an electronegative atom (N, O or F) of another molecule.
- London dispersion forces
- Weak intermolecular forces arising from temporary fluctuations in electron distribution, creating instantaneous dipoles that induce dipoles in neighbouring molecules.
- Ideal gas equation
- pV = nRT, where p is pressure in Pa, V is volume in m^3, n is moles, R = 8.314 J K^−1 mol^−1 and T is temperature in kelvin.
- Avogadro constant
- The number of particles (atoms, molecules or ions) in one mole of a substance, equal to 6.022 × 10^23 mol^−1.
- Molar volume of gas
- The volume occupied by one mole of an ideal gas; approximately 22.7 dm^3 at 273 K and 1.00 × 10^5 Pa, or 22.4 dm^3 at 273 K and 1 atm.
- Partial pressure
- The pressure that a gas in a mixture would exert if it alone occupied the whole volume at the same temperature; equals mole fraction times total pressure.
- Hess's law
- The enthalpy change of a reaction is independent of the route taken, provided the initial and final conditions are the same.
- Standard enthalpy of formation
- The enthalpy change when one mole of a compound is formed from its elements in their standard states at 298 K and 1 bar.
- Bond enthalpy
- The average enthalpy change when one mole of a particular covalent bond is broken in the gaseous state; used to estimate reaction enthalpies.
- Lattice enthalpy
- The enthalpy change when one mole of an ionic solid is formed from its constituent gaseous ions, or the energy needed to separate one mole of solid into gaseous ions.
- Le Chatelier's principle
- When a system at equilibrium is subjected to a change in concentration, pressure or temperature, the equilibrium shifts in the direction that opposes the change.
- Buffer solution
- A solution that resists changes in pH on addition of small amounts of acid or base, usually containing a weak acid and its conjugate base in similar concentrations.
- Solubility product Ksp
- The equilibrium constant for the dissolution of a sparingly soluble ionic solid, equal to the product of the concentrations of its ions each raised to their stoichiometric coefficients.
- Rate-determining step
- The slowest step in a reaction mechanism, which controls the overall rate of reaction and determines the form of the experimental rate law.
- Activation energy
- The minimum energy that colliding particles must possess for a reaction to occur; catalysts lower it without altering the enthalpy change of the reaction.
- Half-life (first order)
- The time taken for the concentration of a reactant to fall to half its initial value; for a first-order reaction it is constant and equal to ln2/k.
- SN2 mechanism
- A one-step nucleophilic substitution in which the nucleophile attacks from the side opposite the leaving group, causing inversion of configuration and second-order kinetics.
- Standard electrode potential
- The emf of a cell with the standard hydrogen electrode on the left and the half-cell under standard conditions on the right; measured at 298 K, 1 M and 1 bar.
- Nernst equation
- E = E° − (RT/nF) ln Q, which relates the cell potential to the standard potential and the reaction quotient; at 298 K it becomes E = E° − (0.0592/n) log Q.
- Faraday's laws of electrolysis
- The mass of substance deposited or liberated at an electrode is proportional to the quantity of charge passed and to the molar mass divided by the number of electrons transferred.
- Markovnikov's rule
- In electrophilic addition of HX to an unsymmetrical alkene, the hydrogen atom adds to the carbon atom that already bears the greater number of hydrogen atoms.
- Chiral centre
- A carbon atom bonded to four different groups, giving rise to non-superimposable mirror-image isomers (enantiomers) that rotate plane-polarised light.
- Esterification
- The reversible reaction between a carboxylic acid and an alcohol, catalysed by concentrated acid, producing an ester and water.
- Haber process
- The industrial synthesis of ammonia from nitrogen and hydrogen using an iron catalyst at about 450 °C and 200 atm, balancing rate and equilibrium yield.
- Beer–Lambert law
- The absorbance of light by a solution is directly proportional to the concentration of the absorbing species and the path length through the solution.
- Rf value
- In chromatography, the ratio of the distance travelled by a spot to the distance travelled by the solvent front, used to identify substances.