IB Definitions
CORE
Define the terms relative atomic mass
(Ar) and relative molecular mass (Mr).
relative atomic mass of an element is the weighted mean mass of all the naturally
occuring isotopes of an element relative to the mass of an atom of 12C
6
relative molecular mass is the average mass of the molecules in a given sample of pure
substance relative to the mass of an atom of carbon 12
Define the terms mass number (A),
atomic number (Z) and isotopes of an
element.
The mass number is the total number of protons and neutrons in the nucleus of an atom
The atomic number is equivalent to the number of protons in the nucleus of an atom
Isotopes are atoms which have the same atomic number but different mass numbers (due
to the presence of different numbers of neutrons in their nuclei)
Define the terms first ionization energy
and electronegativity.
The first ionization energy is the minimum energy required to remove the
outermost electron from each atom in a mole of gaseous atoms
Electronegativity is a measure of the ability of an atom to attract a pair of electrons
in a covalent bond
Define the terms exothermic reaction,
endothermic reaction and standard
enthalpy change of reaction ( _H Ö ) .
An exothermic reaction is one in which there is an overall negative enthalpy
change (heat is evolved)
An endothermic reaction is one in which there is an overall postive enthalpy
change (heat is absorbed)
The standard enthalpy change of a reaction is the enthalpy change when one mole
of reactants is transformed into products at 298K and 101.3 KPa (1atm)
Define the term average bond
enthalpy.
The average bond enthalpy is the average energy change when 1 mole of a particular
covalent bond is broken to give atoms; reactants and products being in the gaseous
state.
e.g. HCl (g) --> H(g) + Cl(g)
Define the term rate of reaction.
The rate of a chemical reaction is the rate of disappearance of reactants or the
rate of appearance of products. (can be a rate of concentration change, pressure
change, volume change…)
N.B. colour change is an indirect measurement of concentration change
Define the term activation energy, Ea.
Activation energy (Ea) is the minimum energy required for a chemical reaction to
occur
Define acids and bases according
to the Br?sted–Lowry and Lewis
theories.
A Bronsted acid is a proton donor (eg H2O --> H+ + OH -).
A Bronsted base is a proton acceptor (eg H2O --> H3O+)
A Lewis acid is an electron pair acceptor (eg BF3 + NH3 --> BF3.NH3)
A Lewis base is an electron pair donor (eg OH-, NH3, H2O…)
Define oxidation and reduction in
terms of electron loss and gain.
Oxidation is the loss of electrons (eg Fe2+ --> Fe3+ + e- )
Reduction is the gain of electrons
(eg Cr6+ in : 14H+(aq) + Cr2O72-(aq) --> 2Cr3+(aq) + 7H2O(l))
Define the terms oxidizing agent and
reducing agent.
Oxidising agent is a substance which will usually easily remove electrons from other
substances in a redox reaction (eg halogens, O2, Ag+ --> Ag(s) …).
Reducing agent is a substance which will usually easily lose electrons to other
substances in a redox reaction (eg Al in : 2Al(s) + Fe2O3 (s) ---> 2Al2O3 + 2Fe
N.B. Things which are easily reduced are good oxidising AGENTS
Things which are easily oxidised are good reducing AGENTS
HL
Define the term ligand.
A ligand is an molecule or ion capable of donating a pair of electrons to a central
metal atom or ion
(eg CO in Ni(CO)4, Cl in [NiCl4]2- , You may see en (ethylene diamine) and edta
(ethylene diamine tetra-acetic acid). These are also ligands)
Define and apply the terms standard
state, standard enthalpy change of
formation (_H ) f
Ö and standard
enthalpy change of combustion
(_H ) c
Standard state is the accepted form of the substance at 298K and 101.3KPa
(1atm) (eg graphite for carbon and not diamond, O2 for oxygen and not O3)
Standard enthalpy change of formation is the enthalpy change when one mole of a
substance is formed from its elements in their standard states. Reactants and
products at 298K and 101.3 Kpa (1 atm)
e.g. ΔHfo C(graphite) =0 KJ mol-1, ΔHfo S8 = 0 KJ mol-1,
ΔHfo SO2 = -296.84 KJ mol-1
Standard enthalpy change of combustion is the enthalpy change when one mole of
a substance is completely burned in oxygen. Reactants and products at 298K and
101.3 Kpa (1 atm)
S(s) + O2 (g) --> SO2(g)
ΔHco = -296.84 KJ mol-1
N.B. for reactions of elements with oxygen ΔHco equals ΔHfo
Define and apply the terms lattice
enthalpy and electron affinity.
The lattice enthalpy is the energy evolved when one mole of an ionic
compound is formed from gaseous ions under standard conditions
Electron affinity is the energy change that occurs when an electron is added to a
gaseous atom or ion
Define the term standard electrode
potential (Eo )
The standard electrode potential is the potential of a half cell compared to the
standard hydrogen electrode (SHE) at 298K and 101.3 KPa (1atm). All solutions at
a concentration of 1M
Options
Human Biochemistry
Define the term iodine number
Iodine number is : The number of moles of I2 reacting with one mole
of fat/oil?
Chemistry in industry and technology
Define the term nanotechnology
Nanotechnology involves research and technology
development at the 1 nm - to - 100 nm range.
Nanotechnology creates and uses structures that
have novel properties because of their small size.
Nanotechnology builds on the ability to control or
manipulate at the atomic scale.”
Food chemistry
Define the term antioxidant.
An antioxidant is a substance that delays the onset or slows the
rate
of oxidation. It is used to extend the shelf life of
food.
Define a genetically modified (GM)
food.
A genetically modified food is one derived or
produced from a genetically modified organism.
The food can be substantially different from or
essentially the same as the conventional food, in
terms of composition, nutrition, taste, smell, texture
and functional characteristics.