Caesium Fluoride

Born Haber Cycle.

CsF

kJmol^-1

Lattice enthalpy

Enthalpy of formation

Enthalpy of atomisation (Cs)

Bond dissociation energy (F-F)

First ionisation energy

First electron affinity

– 756.9

– 553.5

76.5

+ 39.7

+ 375.7

REQUIRED

Born-Haber Cycle

We begin by placing the correct formula of the ionic compound at the bottom -------
- where the enthalpy is lowest, but not zero: CsF
NOTE THAT STATE SYMBOLS MUST BE INCLUDED THROUGHOUT

The enthalpy of formation ∆_fH is our first change ---------
Forming the compound from its elements
in their standard states
Cs _(s) + 0.5F_{2 (g)} → CsF_(s)
This reaction is EXOTHERMIC
- so the arrow points down!

2 steps to change
Cs_(s) into Cs ⁺_(g)

Enthalpy of atomisation of Caesium ∆_aH
Cs _(s) → Cs _(g)

First ionisation energy
IE₁

2 steps to change
0.5 F_{2 (g)} into F^-_{(g)
First: Half the Bond Enthalpy}

Bond Enthalpy of F-F
but divided by 2
as half a mole of F-F bonds broken

First Electron Affinity

Lattice Enthalpy

Calculation of EA₁ of Fluorine.........

Caesium Fluoride
CsF

Sodium Oxide
Na₂O

Magnesium Bromide
MgBr₂

Calcium Oxide
CaO