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Chemical Energetics Chemistry A Level CIE
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Chemical Energetics Chemistry A Level CIE
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192↳2=
E
↳
III
Lattice Energy Born Haber Cycles
bond breaking -
endothermic
bond formation - exothermic
· AH = ( -
>
bond formation > bond breaking
· DH = (t)
bond breaking > bond formation
standard enthalpy change of reaction enthalpy change when the amounts of reactants shown in the
:
stoichiometric equation react to give products under standard conditions
-standard enthalpy change of formation :
enthalpy change when one mole of a compound is formed
from its elements under standard conditions
e x
.
: 2 Fe(S) +
102(9) -> FezOzCS) BHf= H
cigraphites + 29(5) +> CS2(e) DHf=(H)
standard enthalpy change of combustion :
enthalpy change when one mole of a compound is burnt
in excess
250 290K
oxygen under standard conditions ,
1 atm
-standard enthalpy change of neutralisation :
enthalpy change when one mole of water is formed by
the reaction of an acid and alkali under standard conditions (always exothermic
-enthalpy change of atomisation
:
enthalpy change when one mole of gaseous atoms is formed from
its element under standard conditions & Must be endothermic labsorb solid -
gas)
,
LiCS) -> LiCg) BHat (H)
:
e x
.
=
C1219) -> C1 (g) DHat =
(H)
, Hatt= DHatmetal +
DHatNM +IEm + EANM
an ionic compound
Lattice Energy
:
enthalpy change when I mole of is formed from its gaseousions
under standard conditions
e x
.
:
Nat (g) +
C1-19) -> NaCICS) DHatt= -
+
Mg2 (g) +
2C1- (g) -
MgClz(S) DHlatt = If
2A13 30219) A1z03 (S)
+
19) + -
DHlatt= -
Mg2 (9) 02-(9) M90(S)
+
+
-> &Hatt= -)
·
Electron Affinity
the energy change when a gaseous non metal atom accepts one electron
-First electron affinity :
enthalpy change when I mole of electrons is added to I mole of gaseous atoms
to form one mole of gaseous 1-ions under standard conditions
-second electron affinity :
enthalpy change when I mole of electrons is added to I mole of gaseous--ions
to form one mole of gaseous 2-ions under standard conditions
First : subsequent :
Formation of bond -) and repel - need to supply energy to form
(->
subsequently , .
First exothermic , then endothermic :
Energy needs to be absorbed to overcome Electrostatic forces of
(t)
!
masukin energy ke
Attraction between negative charged electrons and negative ions
shell yg less energy
negatives
-
S(g) e S (9) 200 trend 1s+ EA down the group decrease cless
-
+
->
-
S
-
(9) 640
-
5-(9) e F
-
+ -
+
FC e
more energy
52 -(9) Cl
440
-
S(9) +
ze - +
Br masuk shell
larger
radius Cl
yg higher
I
-e- energy ,
We
I di release
* why Hat of Cl half of its bond energy (+244K)/MOl ↓ IeSS
weaker nuclear
E((219) -- (I(g) Attraction
I (4) So BHat =
+ 122 LE
=
BHF-DH1
I gaS LE =
DHF-(IDHqt+IDHatNM+IlEm +ZEANm)
Cl gas yellowish green Add e- to i not favourable,
there's repulsion , to overcome
Br liquid reddish-brown
the repulsion bond energy
I solid black (gas :
purple , liquid
:
dark browns
D Hat of He =
0K) /Mol
Element Always zero
Kr , Ar , etc
All noble gases ,
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