# Calculating lattice energy on ionic compound

• flemonster
In summary, by using heats of formation, ionization energies, and electron affinity, we can calculate the lattice energy of CaBr2(s) to be -2376 kJ/mol. However, it is important to consider the number of bromine atoms in the dissociation enthalpy of Br(g) to accurately balance the reaction equation and obtain the correct lattice energy.
flemonster

## Homework Statement

Given the following thermodynamic data, calculate the lattice energy of CaBr2(s) caculate the lattice enegy:

(A) Δ°Hf CaBr2(s) = -675 kJ/mol
(B) Δ°Hf Ca(g) = 179 kJ/mol
(C) Δ°Hf Br(g) = 112 kJ/mol
(D) 1st ionization energy of Ca = 590 kJ/mol
(E) 2nd ionization energy of Ca = 1145 kJ/mol
(F) Electron affinity of Br = -325 kJ/mol

## Homework Equations

Heats of Formation + ionization energies + electron affinity - lattice energy = heat of formation

## The Attempt at a Solution

(B) + (C) + (D) + (E) + (F) + Lattice Energy = -675

solving for lattice energy:

[179 + 112 + 590 + 1145 + -325] + Lattice Energy = -675

Lattice energy = -675 - 1701

Lattice energy = -2376 kJ/mol

I think I am going wrong with something in the calculations of the energy bromine contributes to the equation. I know bromine is diatomic but I'm not sure how to incorporate that into the equation. I don't want you to give me the answer because I really want to be able to do this on my own but anything you can point out that can get me in the right direction are appreciated.

You are not following stoichiometry - you need to deal with two Br atoms all the time. 112 kJ/mol for Δ°Hf Br(g) is a dissociation enthalpy - but it produces just one Br atom, and you need two.

It should became obvious if you will try to write a "reaction equation" - after all, Hess law is just a way of dealing with the energy conservation. Mass conservation and charge conservation are used to balance reaction equation, same thinking can be applied to the energy conservation.

## 1. How is lattice energy calculated for an ionic compound?

The lattice energy of an ionic compound is calculated by using Coulomb's law, which states that the potential energy of two charged particles is directly proportional to the product of their charges and inversely proportional to the distance between them.

## 2. What factors affect the lattice energy of an ionic compound?

The lattice energy is affected by the charges of the ions involved, the distance between the ions, and the size of the ions. As the charges of the ions increase, the lattice energy increases. Similarly, as the distance between ions decreases, the lattice energy increases. The size of the ions also plays a role, with smaller ions having a greater lattice energy than larger ions.

## 3. Can the lattice energy of an ionic compound be negative?

No, the lattice energy of an ionic compound cannot be negative. It is always a positive value, as the attraction between the oppositely charged ions results in a decrease in potential energy.

## 4. How does the lattice energy affect the stability of an ionic compound?

The lattice energy is a measure of the strength of the bonds between ions in an ionic compound. A higher lattice energy indicates a stronger bond, making the compound more stable. Therefore, compounds with higher lattice energies tend to have higher melting and boiling points, as well as greater overall stability.

## 5. How is lattice energy related to the strength of an ionic bond?

The lattice energy is directly related to the strength of an ionic bond. As the lattice energy increases, the strength of the bond between the ions also increases. This is because a higher lattice energy means there is a greater attraction between the ions, resulting in a stronger bond.

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