# Use the following data (in kJ/mol) to estimate the standard enthalpy of formation (in kJ/mol) for hypothetical compound CsF2 in the solid state.

Lattice energy of CsF2 -2347
First ionization energy of Cs 375.7
Second ionization energy of Cs 2422
Electron affinity of F -328
Bond energy of F2 158
Enthalpy of sublimation of Cs 76.1

How am I supposed to put all of that information together? Can someone please start me...

deltaH = lattice energy+first IP+second IP+ (2xEA) + bond energy F2 + deltaH sub = ??

Write each equation above, then add them together to make sure that the signs are right and that all of them add together to give you the equation you want.
That is,
Cs(s) ==> Cs(g) 76.1 kJ/mol
Cs(g) ==> Cs^+(g) + e. +375.7 kJ/mol
Cs^+(g) ==> Cs^+2(g) + e 2422 kJ/mol
F(g) + e ==> F^-(g) -328 kJ/mol and you will need 2 mols of this which multiplies the -328 also.
etc.
What you want is for the final equation, after everything cancels, is
Cs(s) + F2(g) ==> CsF2(s)

There is a good site on the Internet. Go to www.google.com and look for Born-Haber cycle.
Post your work if you run into trouble. Check my work carefully. It is easy to add too many + signs and () in the wrong place.

I think I still haven't grasped some concepts to fully understand the problem. Right now I am reading the book... so when I come back to the problem, I will ask again if I need any more help from what you already provided me with.

Thanks for the help and site :)

OK. Please be specific about what you don't understand if you repost. Here are two web sites that help a great deal. Good luck. http://chemistry.bd.psu.edu/jircitano/BH.html
http://www.chem.uncc.edu/faculty/murphy/1251/slides/C18a/sld010.htm

9 months ago

## The problem you are trying to solve involves estimating the standard enthalpy of formation for the hypothetical compound CsF2 in the solid state. To do this, you need to consider several factors, such as the lattice energy, ionization energy, electron affinity, bond energy, and enthalpy of sublimation.

Here is a step-by-step guide to help you put all of the information together:

1. Start by writing down the equations for the various processes involved in the formation of CsF2.

2. The first equation represents the enthalpy of sublimation of Cs:

Cs(s) â†’ Cs(g) Î”H(sub) = +76.1 kJ/mol

3. The second equation represents the first ionization energy of Cs:

Cs(g) â†’ Cs+(g) + e- Î”H(ionization1) = +375.7 kJ/mol

4. The third equation represents the second ionization energy of Cs:

Cs+(g) â†’ Cs2+(g) + e- Î”H(ionization2) = +2422 kJ/mol

5. The fourth equation represents the electron affinity of F:

F(g) + e- â†’ F-(g) Î”H(electron affinity) = -328 kJ/mol

Note: Since you're dealing with two moles of F in the formation of CsF2, you need to multiply the electron affinity by 2.

6. The fifth equation represents the bond energy of F2:

F2(g) â†’ 2F(g) Î”H(bond energy) = +158 kJ/mol

7. The final equation represents the formation of CsF2:

Cs(s) + F2(g) â†’ CsF2(s) Î”H(formation) = ?

8. To calculate the standard enthalpy of formation, add up all the enthalpy changes and make sure the equations are balanced:

Î”H(formation) = Î”H(sub) + Î”H(ionization1) + Î”H(ionization2) + (2 * Î”H(electron affinity)) + Î”H(bond energy)

9. Plug in the values given in the problem:

Î”H(formation) = 76.1 + 375.7 + 2422 + (2 * -328) + 158

10. Calculate the sum.

11. The final answer will give you the estimated standard enthalpy of formation for CsF2 in the solid state.

Remember to double-check your work and make sure all the signs and units are correct.

If you come across any specific questions or need further assistance, feel free to ask.