Calculating Enthalpy of Formation of CaF Using Born-Haber Cycle

[Turkish]

I have a question which I must do yet I can't manage to solve it, any help will be appreciated.

It would be theoretically possible for calcium to forma fluoride CaF containing Ca+ ions and the F- ions in equal numbers. Assuming that the lattice enthalpy of the hypothetical compound is similar to that of NaF (+891 kJ mol ^ -1 ), use a Born-Haber cycle to calculate its enthalpy of formation using the data below

Data:

Enthalpy of atomisation of Ca : +193 kJ Mol ^ -1
F-F Bond enthalpy : +158 kJ Mol ^ -1
First Ionisation Energy of Ca: + 590 kJ Mol ^ -1
Electron Affinity of Flourine: -348 kJ Mol ^ -1

The enthalpy of formation of CaF2 is -1214 kJ mol ^ -1. Use this to explain why it is not possible to produce CaF even if two moles of calcium are reacted with one mole of flourine gas.

 

[siddharth]

Turkish, what have you tried so far?

 

[Blueshift5]

The enthalpy of formation of a compound is the energy required to form one mole of the compound from its constituent elements in their standard states. In this case, we are trying to calculate the enthalpy of formation of CaF using a Born-Haber cycle, which involves a series of steps to determine the overall energy change.

The first step in the Born-Haber cycle is to calculate the enthalpy of atomization of calcium, which is the energy required to break one mole of calcium atoms into gaseous atoms. This value is given as +193 kJ mol^-1 in the data provided.

The next step is to calculate the bond enthalpy between two fluorine atoms, which is the energy required to break one mole of F-F bonds. This value is given as +158 kJ mol^-1 in the data provided.

The third step is to calculate the first ionization energy of calcium, which is the energy required to remove one mole of electrons from one mole of gaseous calcium atoms. This value is given as +590 kJ mol^-1 in the data provided.

The fourth step is to calculate the electron affinity of fluorine, which is the energy released when one mole of electrons is added to one mole of gaseous fluorine atoms. This value is given as -348 kJ mol^-1 in the data provided.

Finally, to calculate the enthalpy of formation of CaF, we must add all of these energies together and take into account the enthalpy of the lattice formation of CaF2, which is given as -1214 kJ mol^-1 in the data provided.

Based on these calculations, we can see that the energy required to form CaF is much higher than the energy released when forming CaF2. This is why it is not possible to produce CaF even if two moles of calcium are reacted with one mole of fluorine gas. The energy required to form CaF is simply too high, and the reaction would not be thermodynamically favorable.

In conclusion, the Born-Haber cycle is a useful tool for calculating the enthalpy of formation of a compound, and in this case, it helps us understand why it is not possible to produce CaF despite the theoretical possibility of forming such a compound.