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# This is a really tough problem

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Joined: Sep 2005
This is a really tough problem

I could really use some help on this one. I guess it's what I deserve leaving everything to Sunday night. Anyways, I'v looked through my book to try to find out how to do it and I'm compleatly stumped. Could you guys look at it, and if you know how to do it, explain it to me? I'd really appreciate it if you could. Here it is:

Use the following information to estimate ∆H°f for sodium chloride.

Na(s)+ 1/2Cl2(g) → NaCl(s)

Lattice energy is –786 kJ/mol
Ionization energy for Na is 495 kJ/mol
Electron affinity of Cl is -349 kJ/mol
Bond energy of Cl2 is 239 kJ/mol
Enthalpy of sublimation for Na is 109 kJ/mol

Sorry if it's a little hard to understand, the sub-and superscript didn't follow over when I pasted it.

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Forgot to add this earlier- it's due on Tuesday, so the earlier, the better.

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Joined: Mar 2005

We haven't done that yet and things in Chemistry don't come to me until my teacher explains. The only thing that I could find is that the change in Enthalphy (&H) is equal to the energy before minus the energy after. Please assume that & is delta.

Or another possibility, &H = Hproducts - H reactants

Or, yet another possibility, though I'm not sure how it'll help, but it's worth a shot, &H = &E + P&V where E is the internal energy of the system, P is pressure, and V is volume.

Although, the more I look, I'm starting to think it's in the Themochemistry chapter. The equation is (it's complicated to type here, but & is delta and \$ is sigma):

&H = \$Np&Hproducts - \$Nr&Hreactants

Umm, basically it's the number of moles of products times the combined enthalpies of the products minus the same thing for reactants. There's a chart in the back giving most of the enthalpies (or at least there is in the fifth edition), but Na and Cl2 are going to have enthalpies of zero since they are in their standard states. But, I'm not entirely sure you're allowed to use this.

Anyways, sorry I can't be of more help, but I hope that you get the answer.

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Joined: Sep 2005

Thanks, anyways, pianogirl. I don't think that's what I need to do, and that the answer is probably connected with all of the givens.

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Bonds broken-bonds formed

Reactants-Products

That's what you need, I did this 2 chapters ago.

I would work it out for you but I am short on time, sorry

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