Question

By using data from Appendix C, Figure 7.11, Table 7.5, and the value of the second ionization energy for Ca, 1145 kJ/mol, calculate the lattice energy ofCaF₂.

Electron Affinities in kJ/mol

Figure 7.11

Answer 1

Use concept of Born-Haber cycle. That means split up the process
of formation of the salt from its elements into steps, for which the enthalpy change is known. The sum of the enthalpy changes equals the enthalpy offormation of the salt.

The asked lattice energy represents one of the steps. Since we know the enthalpy of formation and the enthalpy of all other steps, we can calculate fromthe over all enthalpy of the process.


Steps:
1. atomization of calcium
Ca(s) + F2(g) ? Ca(g) + F2(g)
Enthalpy of this step is the sublimation enthalpy of calcium
?H1 = 121kJ/mol

2. ionization of calcium
Ca(g) + F2(g) ? Ca²?(g) + F2(g) + 2 e?
enthalpy of this step is sum of first and second ionization energy
?H2 = 590kJ/mol + 1145kJ/mol = 1735kJ/mol

3. atomization of fluorine
Ca²?(g) + F2(g) + 2 e? ? Ca²?(g) + F(g) + 2 e?
enthalpy of this step is equal to the bond energy of the fluorine molecule:
?H3 = 157kJ/mol


4. ionization of fluorine
Ca²?(g) + 2 F(g) + 2 e? ? Ca²?(g) + 2 F?(g)
enthalpy of this step is equal to the electron affinity of fluorine:
?H4 = -328 kJ/mol

5. formation of solid calcium fluoride
Ca²?(g) + 2 F?(g) ? CaF2(s)
enthalpy of this step is equal to lattice energy:
?H5 = EL

Overall:
Ca(s) + F2(g) ? CaF2(s)
with
?Hf = ?H1 + ?H2 + ?H3 + ?H4 + EL
=>
EL = ?Hf - ?H1 - ?H2 - ?H3 - ?H4
= -1120kJ/mol - 121kJ/mol - 1735kJ/mol - 157kJ/mol - (-328kJ/mol)
= -2805kJ/mol
Source(s):
http://en.wikipedia.org/wiki/Born-Haber_Cycle

Answer 2

I don't no the answer

Answer 3

Using the electron affinity and ionization energy only describe Ca(g)->ca2+(g). And F(g)->F-(g) But the lattice energy is actually ca2+(g)+F-(g)->caf2(s) It is the energy of two charged particles getting closer from a distance of no electrostatic interactions to the distance of forming an ion pair, the potential drop is significant. Born haber cycle is a good experimental formula to obtain lattice energy, or you may use born Lande equation to get a theoretical result of lattice energy.