Lattice Enthalpy
Enthalpy of
Atomisation
produces 1 mole of
gaseous atoms
DIATOMIC
½X2
Bond Dissociation
Enthalpy
DIATOMIC
twice enthalpy of atomisation
First Electron
Affinity
Second Electron
Affinity
EXOTHERMIC
ENDOTHERMIC
GROUP II HALIDES
x2 - as 2Cl atoms etc
GROUP II HALIDES
x2 as 2 Chloride atoms etc
why? electron is being gained by
a species that is already -ve charged
(there is repulsion)
Lattice Enthalpy
ENDOTHERMIC
always positive
- energy needed
- overcome attractive forces
between ions - separate them
values increase as
move down group 7
- size of halide ion increases
- less attraction between ions
- bonds easier broken
- value lower
Standard
Conditions
298K
100kPa
conc. 1 mol dm-3
Standard Enthalpy
of Formation
EXOTHERMIC
energy given out
when bonds are formed
Born-Haber Cycles
Group I Halide
- enthalpy of formation
- atomise M
- ionise (IE) M
- atomise NM
- ionise (EA) NM
- lattice enthalpy
Group II Halide
- enthalpy of formation
- atomise M
- first ionisation of M
- second ionisation of M
- 2x atomise NM
- 2x ionise (EA) NM
- lattice enthalpy
Group II Oxide
- enthalpy of formation
- atomise M
- first ionisation of M
- second ionisation of M
- atomise NM
- 1st electron affinity of NM
- 2nd electron affinity of NM
- lattice enthalpy
Dissolving Compounds
in Water
standard enthalpy
change of solution
process of dissolving can
be EXOTHERMIC or ENDOTHERMIC
temperatures increase + decrease
for different reactions
when ionic
compound dissolves:
- LATTICE ENTHALPY
energy needed to break up
lattice + separate +ve and -ve ions
(ENDOTHERMIC)
- HYDRATION ENTHALPY
energy released when ions form
bonds with water molecules
(EXOTHERMIC)
different ions = different ∆hydH
GROUP II HALIDES
2x ∆hydH as 2 halide ions
- as ionic radius decreases
- value of ∆hydH becomes more negative
- smaller ions experience more attraction on water molecules
- more energy released
- as ionic charge increases
- value of ∆hydH becomes more negative
- greater attraction for water molecules
- more energy released