Chemistry Born-Haber Cycles Help
Hey Basil, in need of some chemists . I have a couple problems regarding Born-Haber Cycles and I am confused about what to do. I don't really know how to go about arriving at the answer and how to write the equations which it asks to do. If someone can maybe help me solve these I will greatly appreciate it. I'm sorry, I feel like such a bother, it's just that I don't get these types of problems =(. Here are some of my problems that I am having trouble with. There were 10 problems total and I managed to do six of them. These four; however, have got me stumped. :
1) Given the following information, find the lattice energy for LiF (s).
Enthalpy of sublimation of Li (s) = 161 kJ/mol
First Ionization energy for Li (g) = 520 kJ/mol
Bond dissociation energy for F2 (g) = 154 kJ/mol
First Electron Affinity for F (g) = -328 kJ/mol
Standard Enthalpy of Formation of LiF (s) = -617 kJ/mol
As you work this problem, practice writing the equations that are associated with each of the energy changes given above.
2) Use the following data to find the value for the Second Electron Affinity for oxygen.
Standard Enthalpy of formation of MgO (s) = -602 kJ/mol
First Ionization Energy for Mg (g) = 150 kJ/mol
Second Ionization Energy for Mg (g) = 2180 kJ/mol
Bond dissociation energy for O2 (g) = 494 kJ/mol
Lattice Energy for MgO (s) = -3916 kJ/mol
First Electron Affinity for O (g) = -141 kJ/mol
Enthalpy of Sublimation of Mg (s) = 150 kJ/mol
As you work this problem, practice writing the equations that are associated with each of the energy changes given above.
3) The standard enthalpy of formation of LiI (<--after Li that is a capital i) (s) is -272 kJ/mol. The first ionization energy of lithium is 520 kJ/mol and the first electron affinity of iodine is -295 kJ/mol. The bond dissociation energy of iodine is -295 kJ/mol, the enthalpy of sublimation of iodine is 61.1 kJ/mol and the lattice energy of LiI (s) is -753 kJ/mol. Use these data to find the standard enthalpy of sublimation of Li (s).
As you work this problem, practice writing the equations that are associated with each of the energy changes given above.
4) The lattice energy for KCl (s) is -690 kJ/mol and the first ionization energy for potassium is 419 kJ/mol. If the first electron affinity of chlorine is -349 kJ/mol, the bond energy of chlorine is 239 kJ/mol and the enthalpy of sublimation of potassium is 64 kJ/mol, what is the value for the standard enthalpy of formation of KCl (s)?
As you work this problem, practice writing the equations that are associated with each of the energy changes given above.
Again, thank you so much for any help. I really appreciate it. =)
4 Comments • Newest first
Oh I see, thanks a lot. I'm gonna try to apply that to the others and see what I get. Thanks again =)
All of these problems are similar in concept.
[1] Finding lattice energy for LiF(s) means: Li+ + F- ---> LiF(s)
___so from that you want to devise a mechanism from Li(s) and F2(g) so that you will end up with Li+ and F- ions:
__________Li(s) ---> Li(g) __________H = 161 kj/mol (enthalpy of sublimation)
_________ Li(g) ---> [Li+] + 1e- _____H = 520 kj/mol (first ionization energy)
_____ 1/2 F2(g) ---> F(g) __________ H = {154/2} kj/mol* (bond disassociation)
_____ F(g) + 1e- ---> [F-] __________H = -328 kj/mol (first electron affinity)
___[b][Li+] + [F-] ---> LiF(s) ______ H = [x] kj/mol (lattice energy)[/b]
==========================================
Li (s) + 1/2 F2(g) ---> LiF(s) ________H = -617 kj/mol (standard enthalpy formation)
From there you just do some math to calculate the lattice energy for LiF: [b][x] = -1047 kj/mol[/b].
*Bond dissociation energy for F(g) -> 2F(g) is Hf = 154 kj/mol, since the stoichiometric equation for this involves [1/2 F(g) ---> F(g)] we want to divide the given Hf by a factor of 2
For the rest of the examples you can follow the same patterns to do your calculations.
First, second, third ionization/affinity means the energy required to lose/gain the 1st, 2nd, 3rd electrons.
For example:
Mg(g) ---> Mg+ + 1e- _______first ionization energy
[Mg+] ---> Mg2+ + 1e- _____ second ionization energy
You have to write your reaction and multiply by necessary constant to some of the energy values then add them all up in the end.
Not really sure sorry. But I think it has something to do with adding up the kJ/mol when getting the right equations. =/