Develop a Born Haber cycle diagram for the compound and indicate how you would determine its lattice energy;

a) KF

Answer

First thing I would do would be to write the formation equation for this ionic compound;

The formation equation would be;

K(s) + 1/2F₂(g) ----> KF(s)

Now we need to develop the additional terms that would allow us to find the lattice energy. First let's focus on potassium. What must we do to potassium to convert it to a gaseous ion?

We must convert potassium in the solid state to potassium in the gaseous phase, then we need to ionize one electron off potassium to get K⁺.

K(s) --H_sublimation--> K(g)

then

K(g) ----> K⁺(g) + 1e^- (I.E. for K)

Now lets focus on F₂. How would we convert F₂(g) to F^-(g)?

We must convert the F₂(g) to a F(g), then we need to add an electron to the F(g) atom to form F^-(g).

1/2F₂(g) -----> F(g) (H_{bond energy} for F₂)

then

F(g) + 1e^- -----> F^-(g) (E.A. for F(g))

Now all we need to do is to take the K⁺(g) and F^-(g) to form KF. That is the lattice energy.

Since,

H_formation(for KF) = H_sublimation(for K) + I.E (for K) + 1/2H_{bond energy} (forF₂) + E.A. (for F) + U (KF)

Now we just need to rearrange this equation to solve for U (KF);

U (KF) = H_sublimation(for K) + I.E (for K) + 1/2H_{bond energy} (forF₂) + E.A. (for F) - H_formation(for KF)

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