Born-Haber Cycle for Al2O3

dfghj

I've tried working it out, but I'm totally confused about the different stages - any help please? :redface:

Reply 1

Mustard-man

Velouria

I've tried working it out, but I'm totally confused about the different stages - any help please? :redface:

see attachment... (just substitute for Al2O3)

They are all structured the same, i.e. arrow position (apart from electron affinity).

1) atomisation of aluminium metal to gaseous atoms (2Al)
2) atomisation of oxygen gas molecules to gaseous atoms (3Cl)
3) ionisation of 2Al (3 ionisation energies), the ionisation energies must be multiplied by 2. Then eventually giving (3+) gasous ions
4) Electron affinity of 3O, first electron affinity is exothermic, second is endothermic, therefore the enodthermic arrow must be pointing the opposite way to the exothermic arrow. The electron affinitiy energies must be multiplied by 3
5) Lattice enthelpy, the formation of a crystalline solid from gasous ions.

This might seem unclear, so ask if you have any problems.
I believe this is correct, I say 'believe' as I have not done one of these since last term. Generally they won't ask you to construct a haber cycle for something as hard as aluminium chloride. Usually they just stick the MgCl2.