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# Born Haber Cycle of CaO confusion? Watch

1. I got all the steps up until Ca2+ + O- + e-

I don't understand why the arrows go in the direction that they do, (more specifically why the arrow goes down for Ca2+ + O- + e- then back up)

Also, why is there only one e- in Ca2+ + O- + e- ? If Ca2+ has undergone 2nd IE, then 2 e- has previously been produced. Did the oxygen take one of those electrons during 1st electron affinity?
2. If you recall that ∆H electron affinity means the enthalpy change when each atom in one mol of gaseous atoms gain an electron to form one mol of gaseous 1- ions then applying it here , since oxygen forms a 2- ion, it uses those electrons available so yes.

Putting it in concept sometimes helps

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3. (Original post by Lemauricien)
If you recall that ∆H electron affinity means the enthalpy change when each atom in one mol of gaseous atoms gain an electron to form one mol of gaseous 1- ions then applying it here , since oxygen forms a 2- ion, it uses those electrons available so yes.

Putting it in concept sometimes helps

Posted from TSR Mobile
So the next step 'Ca2+ (g) + O2- (g)' has no electrons present because the oxygen has taken up 2 electrons?
4. Theres a downward arrow because the 1st electron affinity is exo and it goes back up because the 2nd electron affinity is endothermic. Is this correct?
5. In a simplification: thecalcium has released two electrons in becoming ionised to Ca2+. For the purposes of the calculation theoxygen picks up these two electrons one at a time. Putting one electron onto the oxygen (1st EA) actuallyreleases energy as oxygen has a high attraction for electrons, hence a negative delta H(arrow goes down). However gaining thesecond electron (2nd EA) requires an input of energy (positive deltaH, arrow goes up) as the electron is now being gained by an electron richoxygen ion.
6. (Original post by Mina_)
So the next step 'Ca2+ (g) + O2- (g)' has no electrons present because the oxygen has taken up 2 electrons?
Correct

Posted from TSR Mobile
7. (Original post by Mina_)
Theres a downward arrow because the 1st electron affinity is exo and it goes back up because the 2nd electron affinity is endothermic. Is this correct?
If you look carefully, they can point any way, as long as it's facing down , I think they just do that for making it look neater tbh

Posted from TSR Mobile
8. (Original post by Mina_)
Theres a downward arrow because the 1st electron affinity is exo and it goes back up because the 2nd electron affinity is endothermic. Is this correct?
This is correct ...

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Updated: June 22, 2016
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