chemistry definitions syllabus/textbook

lattice energy

energy released when one mole of an ionic compound is formed from gaseous ions, under standard conditions

electron affinity

energy change associated with addition of electron to gaseous atom or ion

entropy

measure of the disorder or randomness of a system or surroundings

gibbs free energy

energy of a system that is available to do work at a constant temp and pressure

standard electrode potential

voltage produced by a half cell compared with a standard hydrogen electrode under standard conditions

standard cell potential

potential difference if voltage between 2 half cells under standard conditions

standard hydrogen electrode

half cell consisting of inert platinum electrode immersed in 1M HCl with hydrogen gas at 1atm, bubbling through the solution. used as the standard of a cell potential of zero.

enthalpy change of hydration

enthalpy change when 1 mole of gaseous ions dissolves in enough water to form a dilute solution

enthalpy change of solution

energy absorbed or released when 1 mole of an ionic solid dissolves in enough water to form a dilute solution

enthalpy change of atomisation

enthalpy change when 1 mole of gaseous ions is formed from its element under standard conditions

conjugate pair

an acid and base on each side of an equilibrium equation that are related to each other by difference of a proton

buffer solution

solution that minimises changes in pH when moderate amounts of acid or base are added.

common ion effect

reduction in solubility of a dissolved salt by adding a compound that has an ion in common with the dissolved salt, leading to precipitation

ionic product of water, Kw

equilibrium constant for ionisation of water

partition coefficient

ratio of concentrations of a solute in two different immiscible solvents when an equilibrium has been established

acid dissociation constant, Ka

equilibrium constant for a weak acid

pKa

values of Ka expressed as a logarithm to base 10

pH

hydrogen ion concentration expressed as a logarithm to base 10

solubility product, Ksp

equilibrium expression showing product of concentrations of each ion in a saturated solution of a sparingly soluble salt at 298K, raised to the power of the relative concentrations

rate equation

equation showing relationship between rate constant and concentrations of those reactions that affect the rate of reaction.

order of reaction

power that the concentration of a reactant is raised in the rate equation.

concentration does not affect rate

zero order

rate is directly proportional to reaction concentration

first order

rate directly proportional to square of reactant concentration

second order

half life

time taken for amount/concentration of limiting reactant to decrease to half its initial value

rate constant

proportionality constant in the rate equation

rate determining step

slowest step in a reaction mechanism

transition element

a d block element that forms one or more stable ions with an incomplete d subshell

degenerate orbitals

atomic orbitals at the same energy level

complex ion/complex

central transition metal ion surrounded by ligands

coordination number

number of coordinate bonds formed by ligands to the central transition metal ion in a complex

ligand

molecule or ion with one or more lone pairs of electrons available to donate to a transition metal ion

stability constant, Kstab

equilibrium constant for the formation of a complex ion in a solvent from its constituent ions or molecules

heterogenous catalyst

type of catalyst in a different phase from reactions eg iron in Haber process

homogenous catalyst

type of catalyst in same phase as reactions eg sulfuric acid in formation of ester

racemic mixture

50/50 mix of enantiomers with equal but opposite optical activity, leading to optically inactive mixture

optical activity

effect of an optical isomers interaction with plane polarized light

polymer

long chain molecule made of many repeating units

polyester

polymers whose monomers are bonded to each other via ester link

stationary phase

immobile phase in chromatography that the mobile phase passes over or through

mobile phase

solvent in chromatography process which moves through the column or over paper

retention time

time taken for component in a mixture to travel through the column in GLC or HPLC

retention factor, Rf value

ratio of the distance a component has travelled compared with distance travelled by the solvent front during paper chromatography

TMS, tetramethylsilane

inert volatile liquid used as a reference in NMR, given a chemical shift of zero