Solve this please ?! Thanks!

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1 Answer
Michael
Jun 5, 2018

B

Explanation:

The lattice energy U is the enthalpy change for:

#sf(Na_((g))^(+)+Cl_((g))^(-)rarrNaCl_((s)))#

It is very difficult to measure this directly so we measure this indirectly by constructing a Born - Haber cycle, which is an application of Hess' Law.

Hess' Law states that the overall enthalpy change of a reaction is independent of the route taken.

We construct a Born - Haber cycle:

MFDocs

From Hess' Law you can see that, in energy terms, the red arrows must equal the blue arrow.

You will note that I have divided the bond enthalpy of chlorine by 2 since we are only interested in forming 1 mole of Cl atoms.

So we can say:

#sf(108+496+121-349+U=-411)#

#sf(376+U=-411)#

#sf(U=-787color(white)(x)kJ"/""mol")#

This gives (B) as the correct response.

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