AS Chemistry Definitions

Created by

Brady ☆

Cards (46)

Isotope 
atoms of the same element with different numbers of neutrons and different masses
Ion
a positively or negatively charged atom or group of atoms, where the number of electrons is different to the number of protons
relative isotopic mass
the mass of an isotope compared to the mass of one twelfth of the mass of an atom of carbon-12
relative atomic mass
the weighted mean mass of an atom of an element compared to one twelfth of the mass of an atom of carbon-12
mole
the amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of carbon-12
empirical formula
the formula that shows the simplest whole number ratio of atoms in each element present in a compound
molecular formula
a formula that shows the number and the type of atoms of each element present in a compound
standard solution
a solution of a known concentration
acid
proton donor
base
proton acceptor
alkali
a type of base that dissolves in water to produce OH- ions
water of crystallisation
water molecules that are bonded into a crystalline structure of a compound
oxidation 
loss of electrons
reduction
gain of electrons
reducing reagent
reagent that reduces another species
salt
the product of a reaction where the H+ ions in an acid are replaced by metal or ammonium ions
oxidising agent 
a reagent that oxidises another species
disproportionation
a redox reaction which the same element is both oxidised and reduced
atomic orbital
a region of space around the nucleus that can hold up two electrons with opposite spins
sub-shell
a group of orbitals of the same type within a shell
shell
a group of atomic orbitals with the same principle quantum number
electronegativity
a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
enthalpy 
the heat energy stored in a system
activation energy
the minimum energy required to start a reaction by the breaking of bonds
standard conditions
pressure of 100kPa, temperature of 298K, in a concentration of 1 mol dm-3
standard enthalpy change of reaction
the enthalpy change that accompanies a reaction in the molar quantities expressed in the equation under standard conditions with all reactants in their standard states
standard enthalpy change of combustion
the enthalpy change where one mole of substance reacts completely with oxygen under standard conditions with all reactants and products in their standard states
standard enthalpy change of formation
the enthalpy change where one mole of a compound is formed from its constituent elements in standard states under standard conditions
standard enthalpy change of neutralisation
the enthalpy change that accompanies the reaction of an acid and a base to form one mole of water under standard conditions with all reactants in their standard states
average bond enthalpy
energy required to break one mole of a specific bond by homolytic fission in molecules in a gaseous state
hess’ law
if a reaction can take place by more than one route, and the initial and final conditions are the same, the total enthalpy change is the same for each route
catalyst 
a species that lowers the activation energy of a reaction by providing an alternate route but is not used up in itself
dynamic equilibrium
en equilibrium in a closed system where the rate of forward reaction equals that of the reverse reaction leaving constant concentrations of products and reactants
le chatelier’s principle
when a system in equilibrium is subjected to a change, the system readjusts to minimise the effect of the change
homogenous equilibrium 
an equilibrium in which all species have the same physical state
hydrocarbon 
a compound of hydrogen and carbon only
saturated hydrocarbon
contains single bonds only
unsaturated hydrocarbon
contains a multiple carbon-carbon double bond
aliphatic hydrocarbon 
carbons joined together in straight or branched chains
alicyclic hydrocarbon 
carbons joined together in a ring which is not aromatic