Calculating lattice enthelpy of FeF2

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In summary, the question asks to calculate the lattice enthalpy of FeF2 using the given data: Hlatt (FeCl2) = 2569 kJ/mol, r(Cl-) = 181 pm, and r(F-) = 133 pm. The initial approach was to use the proportionality of Hlatt to the product of the charges and the distance between nuclei. However, since the charges were the same for F and Cl, this did not work. The next attempt was to use the Kapustinskii equation to find the radius of iron, but the issue was isolating the distance between nuclei. The professor stated that this is an easy question and no additional data could be used, so the quadratic equation
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hiturtle
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Calculate the lattice enthalpy of FeF2 using the following data:
Hlatt (FeCl2) = 2569 kJ/mol
r(Cl-) = 181 pm
r(F-) = 133 pm

I started with Hlatt is proportional to [absolute value of the product of charge on cation and anion] divided by the distance between their nuclei. Since the charge on F and Cl are the same, you could equate 2 proportionality equations to get Hlatt FeCl2/Hlatt FeF2 = 133 pm / 181 pm. I realized that this wouldn't work because the proportionality is for the distance between nuclei, not the radius of the anion.

So I tried to use the Kapustinskii equation, thinking that I could find the radius of iron. This didn't turn out well because I don't know how to isolate the distance between nucleus.

My prof said that this is an easy question and you're not allowed to use any other data (ex. enthalpy of sublimation, ionization, etc).
 
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hiturtle said:
So I tried to use the Kapustinskii equation, thinking that I could find the radius of iron. This didn't turn out well because I don't know how to isolate the distance between nucleus.

That's a correct approach - and to be honest, I have no idea where the problem is. Looks to me like just a quadratic equation (after rearranging). Complete the square or start with discriminant - that's a basic HS algebra.
 

1. How do I calculate the lattice energy of FeF2?

The lattice energy of FeF2 can be calculated using the Born-Haber cycle, which takes into account various factors such as ionization energy, electron affinity, and lattice energy. The mathematical formula for calculating lattice energy is: ΔHlattice = ΔHf + ΔHsub + ΔHion + ΔHEA + ΔHhydr + ΔHsol. Here, ΔHlattice refers to the lattice energy, ΔHf is the standard enthalpy of formation, ΔHsub is the sublimation energy, ΔHion is the ionization energy, ΔHEA is the electron affinity, ΔHhydr is the hydration energy, and ΔHsol is the lattice energy of the hydrated compound.

2. What is the significance of calculating lattice energy?

Calculating lattice energy is important in understanding the stability and reactivity of a compound. It helps in predicting the overall energy changes in a chemical reaction and determining the strength of ionic bonds in a compound. Additionally, it is useful in studying the properties and behavior of materials in various fields such as materials science, chemistry, and engineering.

3. How does the size of ions affect lattice energy?

The size of ions has a direct impact on the magnitude of lattice energy. Generally, smaller ions have a higher lattice energy due to stronger electrostatic forces between them. This is because smaller ions have a higher charge density, making them more attractive to each other. On the other hand, larger ions have a lower lattice energy due to weaker electrostatic forces between them.

4. Can lattice energy be modified by external factors?

Yes, lattice energy can be influenced by various external factors such as pressure, temperature, and the presence of other compounds. For example, increasing pressure can decrease the distance between ions, resulting in a higher lattice energy. Similarly, increasing temperature can disrupt the ionic bonds, leading to a decrease in lattice energy. The presence of other compounds can also affect lattice energy by altering the charge distribution and ionic interactions.

5. How accurate are the calculations of lattice energy?

The accuracy of lattice energy calculations depends on various factors, such as the accuracy of input data, assumptions made in the calculations, and the complexity of the system. In ideal conditions, the calculated lattice energy should be close to the experimentally measured value. However, due to the limitations of current theoretical models, there may be some discrepancies between the calculated and actual values.

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