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Summary AQA A level chemistry thermodynamics revision notes
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A helpful and comprehensive set of revision notes covering the entire thermodynamics unit of AQA A level chemistry
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Thermodynamies|7.2 BORN HAB ER CYcLES
Enthalpy change isindependent ot the readicm route toke!.
Enthalpy hanges can be worked out usrng thermohemtod uydes
BornHaber Cycdes
- alculate one
quantiyt the othes we al known
- Elements in standad state hawe 2ero enthapy by detinit:on
Endothermik hanges shown upwads, eo thermie chanqu shown
down wards
Lalculat1ng latliee enthalpy ot tomati oj Nol
Naisy’ Naq) AatHNa i+ 108 kJmol
7Clzi9) Clcg) Aatl°:+ 22lJnot
Na (9)’ Nat 1st 1E t4 46kJ mol
Cliq) te’cli) EA : -344 kJ ml
Nas) 2(, c9)Nallis)
Ntg)e lg
|st 1E Na |st EA Cl
Na cal 1 Na'i9) t I a)
Aattt°c
Na c9 AH°Na
AatH Ne
Nas)
+
Nals)
, H NaCl : -(-344) -(446) - (122) - (10s) - 4)
-788 kJmol!
Sometiases bond dissociatic enthaipyi[ given rathe than
atom1s ation in this case must hae the value
A 20 9) AH :t446 kJ mol"
AatH 248 kJmol
2Ol9)
- Be care; on sompounds Suh as k,0
must doube al K vales ns 2 K atons ue used
, 17.2 BORN HABER CYCLES
Factors attecting lattice enthalpy
© Size ot the on
(harac o the on
Lattie enthalpy ot dsso Ciatin ot Ky0 is less endother mie than No 0
K* On is bigges than Nat
- Eletostatic attract icn between oppositey charged 10ns is weakr
Latiu enthapy ot dissociatcn ot Ma0 s greate than ot My Ue
Ox1de 1m hasa charge qreate than a chlonda son
OXIae 10n atrats mag esium 0n mok
strongy
Lattie enthalpies and bonding
Theoretical vaue - based on petect 1nic model
pertect spherespont charges, only ionu bond1ng
Experimental vaue - calulat ed via Born- Hlabu cyce
retlects the true natue of the bond1ng
Some bonds cOmpownds can have 1onic
onic bond1ng with
addit1onal covalent bond1nq
Polarisaticn and distoction ot
2+ 2
Zn Se 1onic bond- a degree of
coval en y
This ows wheni
posit1ve ion s Sma and highy chged
negative 10n is large and highly chaged
exper1mental value impies some extra ovalent
A greater
bond1ng is present
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