Question

Solve this please ?! Thanks!

Answer 1

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:

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.