QCE Chemistry flashcards
QCE Chemistry · Build recall with a focused review session.
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- Empirical formula
- The simplest whole-number ratio of atoms of each element in a compound, found by dividing moles of each element by the smallest mole value obtained.
- Mole calculation
- n = m ÷ M relates moles to mass and molar mass; used as the central step in stoichiometric calculations involving masses, concentrations or gas volumes.
- Limiting reagent
- The reactant consumed first, determined by dividing each reactant's moles by its stoichiometric coefficient; the smallest quotient limits the amount of product formed.
- Percentage yield
- Actual yield divided by theoretical yield, multiplied by 100; measures how much of the predicted product was actually obtained experimentally.
- Atom economy
- Mass of desired product divided by total mass of all reactants, expressed as a percentage; measures how much reactant mass ends up in the target product.
- Ionisation energy trend
- Increases across a period because effective nuclear charge rises and radius falls; decreases down a group because outer electrons are further out and more shielded.
- Electronegativity
- The tendency of an atom to attract shared electrons in a bond; increases across a period and up a group, and its difference between atoms indicates bond polarity.
- Hydrogen bonding
- A strong dipole–dipole attraction between H bonded to N, O or F and a lone pair on a nearby N, O or F atom, raising boiling points markedly.
- Dispersion forces
- Weak temporary attractions caused by instantaneous dipoles; strength increases with more electrons and greater surface contact between molecules.
- Collision theory
- Reactions occur only when particles collide with energy at least equal to the activation energy and with suitable orientation; this explains effects of temperature and concentration.
- Activation energy
- The minimum energy colliding particles need to rearrange bonds and form products; a catalyst lowers it by providing an alternative reaction pathway.
- Exothermic reaction
- A reaction releasing energy to the surroundings so temperature rises; enthalpy change is negative because products have lower enthalpy than reactants.
- Bond energy calculation
- Enthalpy change equals total bond energies broken minus total bond energies formed; a positive result indicates an endothermic reaction overall.
- Calorimetry formula
- q = mcΔT gives heat absorbed by a solution, with c = 4.18 J g⁻¹ K⁻¹ for water; dividing by moles gives molar enthalpy change.
- Like dissolves like
- Polar and ionic solutes dissolve in polar solvents while non-polar solutes dissolve in non-polar solvents, because similar intermolecular forces allow favourable solute–solvent interactions.
- Dynamic equilibrium
- In a closed system, forward and reverse reaction rates become equal and concentrations stay constant, though both reactions continue at the molecular level.
- Equilibrium constant Kc
- The ratio of product concentrations to reactant concentrations, each raised to its stoichiometric coefficient; only species in solution or gas phase are included.
- Le Chatelier's principle
- When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts to partially oppose that change.
- Catalyst and equilibrium
- A catalyst lowers activation energy and speeds attainment of equilibrium but does not alter the equilibrium position or the value of K.
- pH definition
- pH = −log₁₀[H⁺]; a decrease of one pH unit means a tenfold increase in hydrogen ion concentration in aqueous solution.
- Strong versus weak acid
- A strong acid ionises completely in water, giving high [H⁺]; a weak acid ionises only partially and is described by an acid dissociation constant Ka.
- Oxidation and reduction
- Oxidation is loss of electrons and an increase in oxidation number; reduction is gain of electrons and a decrease in oxidation number.
- Oxidising agent
- A species that accepts electrons from another substance, causing that substance to be oxidised while itself being reduced.
- Titration equivalence point
- The point where acid and base have reacted in exact stoichiometric proportions; at this point n(H⁺) equals n(OH⁻) for a monoprotic acid–base reaction.
- IUPAC naming rules
- Select the longest carbon chain, number to give substituents lowest locants, then name the principal functional group with its suffix.
- Structural isomers
- Compounds with the same molecular formula but different arrangements of atoms, including chain, position, functional group and geometric cis–trans isomers.
- Addition reaction
- A reaction in which two molecules combine to form one product, typical of alkenes where the C=C double bond opens to add atoms.
- Substitution reaction
- A reaction in which an atom or group is replaced by another, typical of alkanes reacting with halogens under ultraviolet light.
- Esterification
- A condensation reaction between a carboxylic acid and an alcohol, catalysed by acid, producing an ester and water.
- Addition polymerisation
- Monomers containing carbon–carbon double bonds join without losing atoms, forming a long-chain polymer; the repeating unit has the same formula as the monomer.
- Condensation polymerisation
- Monomers with two functional groups join by eliminating a small molecule such as water, producing a polymer such as a polyester or polyamide.
- Infrared spectroscopy
- Absorption of infrared radiation causes bond vibrations; characteristic wavenumbers identify functional groups such as O–H and C=O in a molecule.