Saturday, 26 November 2011

Module F325 Definitions

Topic 7 - How far?

No definitions

Topic 8 - Acids and bases

Acid (Bronsted-Lowry)                proton donor

Base (Bronsted-Lowry)               proton acceptor

Strong acid or base                    fully ionised (or dissociated)

Weak acid or base                     partially ionised (or dissociated)

Conjugate acid-base pairs           Two species differing by H+

pH                                            pH = -log[H+]

Kw (ionic product of water)          Kw = [H+][OH-]

Ka (acid dissociation constant)     Ka = [H+][A-]

pKa                                           pKa = -log[Ka]

Buffer solution                           a solution that resists change in pH

Topic 9 - How fast?

Rate of reaction                         rate of change of concentration of reactants or products (units are mol dm-3 s-1)

Order of reaction                        power of reactant’s concentration in the rate equation

Rate constant                             the constant of proportionality, k, in the rate equation

Half-life                                     the time for the concentration of a reactant to fall to half its original value

Rate determining step                 the slowest step (in the reaction mechanism)

Topic 10 - Lattice enthalpy and entropy

Lattice enthalpy                         the enthalpy change that accompanies the formation of one mole of a solid compound from its constituent gaseous ions
e.g.       Na+(g) + Cl-(g) ® NaCl(s)

Enthalpy of neutralisation            the change in enthalpy that occurs when an acid and base undergo a neutralisation reaction to form one mole of water i.e.         H+(aq) + OH-(aq) ® H2O(l)

Enthalpy of solution                    Enthalpy when one mole of an ionic solid is completely dissolved in water
e.g.       NaCl(s) ® Na+(aq) + Cl-(aq) 

Enthalpy of hydration                  Enthalpy change when one mole of gaseous ions is completely dissolved in water
e.g.       Na+(g) ® Na+(aq) or Cl-(g) ® Cl-(aq) 

Topic 11 - Transition elements

Transition element                     a d-block element that forms one or more stable ions with an incomplete set of d electrons

Complex ion                               a central ion surrounded by ligands

Ligand                                       an ion or molecule with a lone pair of electrons able to form a dative covalent bond

Ligand substitution                     a reaction in which one ligand is displaced by another ligand

Co-ordination number                 the number of lone pairs bonded to the central ion

Bidentate ligand                         a ligand that can form two dative bonds because it has two lone pairs

Topic 12 - Electrode potentials

Standard electrode potential        the voltage of a cell when the electrode is connected to a hydrogen electrode under standard conditions

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