Cambridge IAL Chemistry flashcards
Cambridge IAL 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.
- Lattice enthalpy definition
- The enthalpy change when one mole of a solid ionic compound forms from its gaseous ions under standard conditions; it is always exothermic and its magnitude increases with higher ion charge and smaller ionic radius.
- Enthalpy of hydration
- The enthalpy change when one mole of gaseous ions dissolves in water to form one mole of aqueous ions; it is exothermic because ion–dipole bonds form between ions and water molecules.
- Entropy
- A measure of the dispersal of energy or disorder in a system, in J K⁻¹ mol⁻¹; gases have higher entropy than liquids, which have higher entropy than solids.
- Gibbs free energy criterion
- A reaction is feasible when ΔG = ΔH − TΔS is negative; increasing temperature favours an endothermic reaction with positive ΔS because the −TΔS term becomes more negative.
- Rate-determining step
- The slowest step in a multi-step reaction mechanism; the rate equation reflects the species involved in this step, so orders can be deduced from it.
- Order of reaction
- The power to which a reactant concentration is raised in the experimentally determined rate equation; zero order means concentration has no effect on rate.
- Dynamic equilibrium
- A state in a closed system where the forward and reverse reaction rates are equal, so concentrations remain constant although both reactions continue.
- Buffer solution
- A solution that resists pH change on addition of small amounts of acid or alkali, usually made from a weak acid and its conjugate base in comparable concentrations.
- Amphoteric oxide
- An oxide that reacts with both acids and alkalis to form salts, such as aluminium oxide, which gives aluminium salts with acid and aluminates with alkali.
- Thermal stability of Group 2 carbonates
- Stability increases down the group because the larger cation polarises the carbonate ion less, so decomposition temperature rises from magnesium carbonate to barium carbonate.
- Disproportionation
- A reaction in which the same element is simultaneously oxidised and reduced, such as chlorine with cold dilute alkali forming chloride and chlorate(I) ions.
- Ligand
- A species that donates a lone pair of electrons to a central metal ion to form a coordinate bond, for example water, ammonia or chloride ions.
- Coordination number
- The number of coordinate bonds from ligands to the central metal ion in a complex; it is six in octahedral complexes and four in tetrahedral complexes.
- Oxidising power of halogens
- The ability to accept electrons, which decreases down Group 17 as the atoms get larger and the incoming electron is less strongly attracted to the nucleus.
- Silver halide test
- Adding silver nitrate solution acidified with dilute nitric acid gives a precipitate: white for chloride, cream for bromide and yellow for iodide, used to identify halide ions.
- Catalyst in transition metals
- Transition metals and their compounds catalyse reactions by providing an alternative pathway with lower activation energy, aided by variable oxidation states.
- Structural isomerism
- Compounds with the same molecular formula but different structural formulae, giving different physical properties and sometimes different chemical behaviour.
- Stereoisomerism
- Compounds with the same structural formula but different spatial arrangements; includes E–Z isomers about a double bond and optical isomers with a chiral centre.
- Chiral centre
- A carbon atom bonded to four different groups; it produces two non-superimposable mirror-image optical isomers that rotate plane-polarised light in opposite directions.
- Markovnikov's rule
- When a hydrogen halide adds to an unsymmetrical alkene, the hydrogen atom attaches to the carbon that already has the greater number of hydrogen atoms.
- Nucleophilic substitution
- A reaction in which a nucleophile replaces a halogen atom in a halogenoalkane; hydroxide ions in water give alcohols and cyanide ions give nitriles.
- Elimination reaction
- A reaction removing atoms from adjacent carbons to form a double bond; heating a halogenoalkane with ethanolic potassium hydroxide produces an alkene.
- Free-radical substitution
- The reaction of alkanes with halogens in ultraviolet light, proceeding by initiation, propagation and termination steps involving reactive radical species.
- Esterification
- The reversible acid-catalysed reaction of a carboxylic acid with an alcohol to form an ester and water, often carried out under reflux with a sulfuric acid catalyst.
- Tollens' reagent
- Ammoniacal silver nitrate solution, which is reduced to a silver mirror by an aldehyde but not by a ketone, distinguishing the two carbonyl compounds.
- Nitrile formation
- Heating a halogenoalkane with potassium cyanide in aqueous ethanol replaces the halogen with a nitrile group, extending the carbon chain by one atom.
- Concordant titres
- Titres that agree to within about 0.10 cm³ of each other; their mean is used in calculations, and non-concordant values are discarded as anomalies.
- Percentage uncertainty
- The absolute uncertainty of a measurement divided by the measured value, multiplied by 100; using a larger measured quantity reduces the percentage uncertainty.
- Recrystallisation
- A purification technique in which an impure solid dissolves in the minimum volume of hot solvent, then crystallises on cooling, leaving soluble impurities in the filtrate.
- Reflux
- Heating a reaction mixture under a condenser that returns vaporised solvent to the flask, allowing prolonged heating without loss of the volatile solvent.
- Atom economy
- The molar mass of the desired product divided by the total molar mass of all reactants, expressed as a percentage; it measures how efficiently atoms end up in the product.
- Anomalous result
- A measurement clearly outside the trend of the other data, likely caused by an error; it is identified and excluded from a mean, not silently included.