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# Lattice Enthalpy watch

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1. When you're working out the lattice enthalpy for MgO, is it correct to halve the number for the enthalpy change of atomisation of Oxygen?
If your working out lattic enthalpy for MgCl2, it is right to just take the number for the enthalpy change for atomisation of chlorine and double the number for electron affinity...?
are there any other tricky bits of lattic enthalpy to watch out for?
thanku!
xx
2. But isn't enthaply change of atomisation defined as "enthaply change when ONE MOLE of a gaseous atom is formed from the element in it's standard state".

So shouldn't the values quoted really be for the formation of one mole? Meaning oxygen would not have to be halved, and Cl would have to be doubled?
3. to work out the lattice enthalpy for MgO i'm almost certain that you will half the value for enthalpy of atomisation for oxygen as this number is for 1 mole and you only want half a mole

Mg + 0.5O2 --> MgO

i think that would cover most things that could be unexpected in lattice enthalpy, nothing else springs to mind although i havn't started revising this stuff yet.
4. (Original post by allodoxa)
But isn't enthaply change of atomisation defined as "enthaply change when ONE MOLE of a gaseous atom is formed from the element in it's standard state".

So shouldn't the values quoted really be for the formation of one mole? Meaning oxygen would not have to be halved, and Cl would have to be doubled?
yeah but havent u just contradicted yerself there? It IS forming ONE MOLE, but if u have like:

Cl2(g) ----> 2Cl(g) , then arent u atomising 2 MOLES? so therefore have to double it?
5. (Original post by C0nnie)
When you're working out the lattice enthalpy for MgO, is it correct to halve the number for the enthalpy change of atomisation of Oxygen?
If your working out lattic enthalpy for MgCl2, it is right to just take the number for the enthalpy change for atomisation of chlorine and double the number for electron affinity...?
are there any other tricky bits of lattic enthalpy to watch out for?
thanku!
xx
Yeah I gotta agree with you, another tricky part for me is the second electron affinity is endothermic

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