IB HL Chemistry Definitions (not options)

fecofoha's version from 2015-04-12 16:54


Question Answer
Activation Energy (Ea) The minimum energy that colliding species must have before collision occurs in a chemical reaction
Addition PolymerisationUndergone by Alkenes, monomers turn into polymers
AlkaliA base that is dissolved in Water
AllotropesDifferent forms of the same element e.g. Carbon: diamond, graphite and buck minster fullerene
AnodeElectrode at which oxidation occurs
AtomSimplest part of an element that can still be recognised as an element
Atomic numberThe number of protons in the nucleus of an atom
Average bond enthalpyEnergy required to break one mole of gaseous covalent bonds under standard conditions
Avogadro's constant6.02*10^23
Bronsted-Lowry AcidAcid is a H+ donor
Buffer solutionResists changes in pH when small amounts of acid or alkali are added
CatalystSpeeds up the rate of reaction, does not take part in it, provides a pathway with a lower Ea
CathodeElectrode at which reduction occurs
Chiral centreA carbon atom with 4 different atoms or groups attached
Closed systemNo exchange of matter with surroundings
Collision theoryA reaction can only occur when particles collide with the correct orientation and with E>Ea
Condensation reactionTwo molecules join together and eliminate the presence of water
Contact processIndustrial production of Sulphuric Acid
Convergence LimitThe point in a line emission spectrum where the lines form a continuum- identifies ionisation energy
Covalent bondThe electrostatic attraction between a shared pair of electrons and the nuclei of the atoms being bonded
Dative covalent/coordinate bonda type of covalent bond where both electrons come from the same atom
DegenerateDescribes elements with the same energy
Dynamic equilibriumRate of forward reaction= rate of reverse reaction
ElectrolysisBreaking down of a substance in molten state or solution by the passage of electricity through it
Emission spectrum of an atomElectromagnetic radiation given out when an electron falls from a higher energy level to a lower one
Empirical formulaThe simplest whole number ratio of elements in a compound
EnantiomnersOptical isomers
Endothermic reactionHeat is taken in from surroundings. ΔH+
Enthalpy change (ΔH)The heat energy exchanged with the surroundings at constant pressure
ΔH hydThe enthalpy change when one mole of gaseous ions are surrounded by water molecules to form an infinitely dilute solution, under standard conditions
ΔH nThe enthalpy change when one mole of H2O molecules are formed when an acid reacts with an alkali under standard conditions
ΔH solThe enthalpy change when one mole of solvent is dissolved in excess solute to form a solution of infinite dilution under standard conditions
Entropy (S)A measure of randomness or disorder in a system
Standard entropy1 atm, 298K, units JK^-1mol^-1
Exothermic reactionReleases heat, ΔH-
First electron affinityEnthalpy change when 1 electron is added to each atom in 1 mole of gaseous atoms, under standard conditions
Gibbs free energyΔG= ΔH-TΔS, spontaneous: ΔH= -
Free radicalA species with an unpaired electron
Functional group eg. -OH, C=C
Geometrical isomersCompounds with the same structural formula but with differently arranged groups around a double bond or ring
Haber processIndustrial process for the formation of Ammonia
Heterolytic fissionA covalent bond breaks so that both electrons go to the same atom
Homolytic fissionA covalent bond breaks so that one electron goes back to each atom in the bond
Ideal gas equationPV=nRT
Intermolecular forcesForces between molecules
Intramolecular forcesForces within molecules
Ionic bondingThe electrostatic attraction between 2 oppositely charged ions
Ionisation energy The energy required to remove 1 electron from a gaseous atom
IsotopesDifferent atoms of the same element with the same number of protons but a different number of neutrons
ΔH lattThe enthalpy change when 1 mole of ionic compound is broken apart into its constituent gaseous ions under standard conditions
Le Chatelier's principleA system will shift the position of equilibrium in order to minimise the effect of a change
Lewis acidElectron pair acceptor
LigandsNegative ions/neutral molecules that use lone pairs of electrons to bond to transition metal ions to form a complex ion. DCBs formed formed between ligand and TM ions


Question Answer
Metallic bondingThe electrostatic attraction between the positive ions in a metallic lattice and a sea of delocalised electrons
Nucleophilic substitutionA halogenoalkane is attacked by a nucleophile which replaces the halogen atom
Optical isomersSame molecular and structural formula but they are non-superimposable mirror images of each other. Rotate plane polarised light in opposite directions
Percentage error((experimental value - accepted value)/accepted value)*100
Percentage uncertainty(uncertainty/ measured value)*100
pHA measure of the H+ concentration in an aqueous solution. Calculated by -log10[H+]
Pi bondFormed by the sideways overlap of parallel P orbitals. Above and below the internuclear axis
Plane-polarised lightLight that vibrates in one plane only
Relative atomic massThe average mass of the naturally occuring isotopes of an element relative to 1/12 mass of an atom of Carbon-12
Relative molecular mass: The mass of a molecule of a compound relative to the mass of 1/12 of an atom of Carbon-12
Question Answer
Saturated compoundsonly contain single bonds
Sigma bondBonds formed by the head on overlap of atomic orbitals
SN1Substitution nucleophilic unimolecular (1 species in RDS)
SN2Substitution nucleophilic bimolecular (2 species in RDS)
Standard conditions1 atm, 298K
Standard electrode potentialThe voltage of a half cell connected to a standard hydrogen electrode under standard conditions
ΔH°CEnthalpy change when 1 mole of a substance is combusted fully in oxygen under standard conditions
ΔH°FEnthalpy change when 1 mole of substance is formed from its elements in their standard states under standard conditions
ΔH°rEnthalpy change when molar amounts of reactants react together to form products under standard conditions
ΔH°vapEnergy required to turn 1 mole of a liquid into vapour under standard conditions
ΔG°fFree energy change for the formation of 1 mole of substance from its elements in their standard states under standard conditions
STP273K, 1 atm
StereoisomersMolecules with the same molecular formula but the atoms are arranged differently in space
Structural isomers2 or more compounds that have the same molecular formula but different structural formula
Subshell/sub levelA group of degenerate orbitals in an atom
Transition metalsAn element which forms at least one stable oxidation state and has a partially filled d subshell
van der Waals forcesintermolecular forces resulting from temporary instantaneous dipole- induced dipole interactions
Vapour pressureThe pressure exerted by a vapour in equilibrium with a liquid (or a solid)
YieldYield= ((actual yield/theoretical yield)/*100)