Download The Born-Haber Cycle

The Born-Haber Cycle
By Brian M. Lawrence, Ph.D.
Chemistry 111/112 Lecture Slides
Morehouse College
Consider the strongly exothermic reaction between
sodium metal and chlorine gas…
2Na(s) + Cl2(g)
2NaCl (s)
What can we learn about attractive forces between
ions from this relationship? Specifically, how much
energy is tied to the attraction of sodium cations to
chloride anions?
Recall that for state functions ( G, H or S) there
is no path dependence. Imagine, then, the
following.
2Na(g)
Ionization
– 2eEnergy
2Cl(g)
2Na(s) + Cl2(g)
2Na+ (g)
Electron
+ 2eAffinity
2Cl-(g)
2NaCl (s)
This hypothetical pathway is call the Born-Haber
Cycle. It is a useful construct for estimating
coulombic attraction between atoms in compounds.
2Na(g)
Ionization Energy
2Na+ (g)
H°coul
H°subl
2Cl(g)
Electron Affinity
2Cl-(g)
BDE
2Na(s) + Cl2(g)
H°rxn
2NaCl (s)
Using the Born-Haber Cycle in this way, we can
determine a reasonable estimate for the coulombic
attraction between the atoms in almost any ionic
compound. The standard thermodynamic parameters
needed to do this can be found in your textbook.
H°rxn =
H°subl + BDE + IE – EA +
BDE = Bond Dissociation Enthalpy
IE = Ionization Energy
EA = Electron Affinity
H°coul