Summary of Chapter 22 OCR A Level

O 3 / O 2 / 2 I


Chapter 22 -




Enthalpy and Entropy
22 .
I Lattice Enthalpy


lattice enthalpy a measure of the strength of ionic bonding in a
giant
-




ionic lattice

↳
enthalpy charge that accompanies the formation of one more of an ionic


compound from its ions under standard conditions
gaseous
↳
involves ionic bond formation from separate gaseous ions →
exothermic ,
-
ve OH




Factors affecting lattice enthalpy Why might the experimental and

→
Charges on the ions theoretical values differ ?


↳ →
t charge ,
t
enthalpy Most compounds have some

→
The radius of the ions covalent bonding as were as

↳
t enthalpy (
size ,
t closer ionic
bonding
together in lattice ) →
Comparing experimental and


theoretical values can show how



Born -

Haber cycles purely ionic a
crystal is .




GASEOUS IONS

Cicotte
-

→ a
-



Cg ) formation of
O & Standard enthalpy
ions
gaseous
Nacg ) Natcg,
change of formation Of Hot
-


→ + e
endothermic

NAU →
Enthalpy
+
Na A (9)
-




Cgl + →
change when
GASEOUS ATOMS
0
(atomization ] formation ROUTE 2 One mole of a compound is
of

vacs , →
Nacg , Saroyan endothermic lattice enthalpy formed from its elements
bond breaking
ELEMENTS IN
( lattice formation Under standard conditions ,

STANDARD
STATES lattice formation from gaseous ions) with all the reactants and
from elements

Na
+
I uz exothermic products in their standard States .




→ Nau

ROUTE 2


O &
p exothermic
Standard enthalpy of
-


IONIC LATTICE

Atonisation Oar Htt

→ Dat HE is endothermic as bonds are
→
The enthalpy
charge
broken that takes place for the


formation of one more of
gaseous
Atoms from the elements in it

standard State under standard conditions .

, & First ionisation
-0
* First electron He
energy Die H
affinity Den .




→ The enthalpy required to
→
The enthalpy change that
charge
remove one electron from each atom takes place when one electron is

in one more of gaseous It ions .
Added to each atom in one more

of to form more
gaseous atoms one

→
Die hot is endothermic of 2- ions
gaseous .




( energy needed to overcome attraction) .




→ electron affinity is the opposite ( energy
→
Dea Hot is Ekothermic As the

needed to ) electron
being added is attracted
-




electrons
gain in


towards the nucleus .




* successive electron affinities
→
second electron affinities are endothermic

02 (g)
-




O




O (g) 2e
- -

+
2nd electron affinity
&
DEA 2 H
1st electron affinity
't
( endothermic as you
DEAL H need to overcome the

repulsion benveen the

p O electron and already
(g)
- -

+ e
negative ion )




1 .
(a) (i ) first ionisation energy

( ii ) second election affinity
Ciii ) enthalpy charge of formation .




(b) (i ) "
Cag , +02 Cae ,
-




Mg MgO
→
es ,

Cii ) F (g)
-


e → F Cg)
-

+



Natg) te Brcg,
-




ztozcg,
t
( iii ) → 0cg ,
1st IE NAD 1st electronaffinity Br

2 .
(a) A -



formation ( b) -
325


B +496 Nat Cg) Cg )
-

t Br
electron affinity p
-




C Na Cgl Brest
-




Atomization
+




atomism on
-


or O
D -



ionisation Lattice Enthalpy
t 112 of Nasr
f
-




Ato thisAtion
'
NAGI t
z Br . Cs )


Atomisation Na
Lf

1- 108
(C) -




( -

325) -

( 496 ) -

( 112 ) Nacht 's Brass


formation Nasr
-

(108 ) t ( 361 )
- 361
'
752 O Nasr Cs)
-



O
KJ Mol
-

=