A2 level chemistry notes

, Energy
aka lattice

Lattice chapter a
enthalpy


surrounds
F =
To +
system A
&E =
Tot




lattice energy (AHiatt) an ionic compound is formed from its gaseous ions
:


energy change when I mole of

standard conditions

↓
energy given out when ions of opp charges come together

↑ exothermic (bonding together of ions ,
not separation)

↳ large exothermic value shows ionic lattice v stable w respect to gaseous ions


↓ the Hiatt the the ionic bonding in the lattice
more exothermic , stronger

* cannot determine Atlant by direct experiment




AHiatt
+
.
e . Na (g)
g + (1- (g) >
-
NaCI (s) = -787kJ MOl .




# of atomisation (AH) :
standard enthalpy change when I mole of gaseous atoms is formed
from its element under standard conditions

↓ endothermic :
energy is supplied to break the bonds holding the atoms in the element together


e .


g
. (i (s) eLi
(g) 1 Hato =
+ 161k) Mol .
-




z((z(g) =
((g)


electron affinity (EA)
EA ,
Alt when 1 mole of es is added to 1 mole of gaseous atoms to form / mole of gaseous ions with

a
single neg charge under SC
.
.




EA2 2-ions formed
Due to repulsion of
↓ net change exothermic
·
neg
ions + es (requires
energy)


EA ,
exothermic => Az endothermic (and EAz)
RHS elements have ? EA be gain e-to become Stable
*
8 (g) 02 (9) EAz 798k)
-



+ e - = + .




Mol
FA 348k) MOl
-




0 0
=
-




(g)
-

e
+
(g)
.


,




-141 + 198
Overall AH in forming oxide ion : add EA ,
+ FAz :
+
= + 657kJ Mo .

,
,