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Calculate the lattice energy of sodium oxide.

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Calculate the lattice energy of sodium oxide.

Post  pplantblues on Sat Jan 31, 2009 4:26 pm

Calculate the lattice energy (U) of sodium oxide (Na2O) from the followng data:
ionization energy of Na(g) 495 kJ/mol

electron affinity of O(g) for 2 e- 603 kJ/mol

energy to vaporize Na(s) 109 kJ/mol

O2(g) bond energy 499 kJ/mol

Energy change for the reaction -416 kJ/mol Na2O
2Na(s) + 1/2 O2(g)-->>Na2O(s)

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Re: Calculate the lattice energy of sodium oxide.

Post  funion987 on Sat Jan 31, 2009 4:43 pm

This is a Hess's Law problem, so I'm going to write everything out in a reaction. I reversed some of the reactions. Lattice energy is defined as the energy needed to form an ionic compound from its gaseous ions.

Na+(g) + e- --> Na(s) (-495 kJ/mol) reversed

O2- ---> O2 + 2e- (-603 kJ/mol) reversed

Na(g) ---> Na(s) (-109 kJ/mol) reversed

2O(g) ---> O2(g) (-499 kJ/mol) reversed

2Na(s) + 1/2O2 ---> Na2O(s)


From there it's just going through the Hess's law. If you have any questions, post. Sorry I didn't do the whole thing; I just don't really like Hess's law problems.

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Re: Calculate the lattice energy of sodium oxide.

Post  pplantblues on Sat Jan 31, 2009 5:12 pm

I think you have to use the Born-Haber cycle.

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Re: Calculate the lattice energy of sodium oxide.

Post  funion987 on Sat Jan 31, 2009 5:18 pm

I've never used the Born-Haber cycle before, sorry. I've always used Hess's Law. Like I said, I really don't like these problems; they give me a headache.

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Re: Calculate the lattice energy of sodium oxide.

Post  pplantblues on Sat Jan 31, 2009 5:34 pm

Oh ok. Thanks anyways. I know what you mean. They give me a headache too. lol

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