# Lattice Energy - Hard question - I keep getting wrong answer

• stacker
In summary: In your problem, K and I are both metal atoms, so V would be the sum of their enthalpies of vaporization. It looks like you may have made a mistake when plugging in the values for heat of sublimation, as the correct answer for lattice energy should be positive. Double check your calculations and make sure you are using the correct values for each variable.
stacker

## Homework Statement

What is the lattice energy of KI? Given the information below.

Heat of formation for KI = -328 kJ/mol

Heat of sublimation for K = 89.20 kJ/mol

Ionization energy for K = 419 kJ/mol

Bond dissociation energy for I2 = 149 kJ/mol

Electron affinity for I = - 295 kJ/mol

Heat of sublimation for I2 = 48.30 kJ/mol

I used Born-Haber's law: Delta H of formation = .5*Delta Dissociation + Delta H of sublimation + Ionization Energy + Electron Affinity + Lattice Energy

## Homework Equations

Born-Haber's law = Delta H of formation = .5*Delta Dissociation + Delta H of sublimation + Ionization Energy + Electron Affinity + Lattice Energy

## The Attempt at a Solution

I used Born-Haber's law: Delta H of formation = .5*Delta Dissociation + Delta H of sublimation + Ionization Energy + Electron Affinity + Lattice Energy

-328 = (89.20 - 48.30) + .5 (149) + 419 - 295 + Lattice Energy

Lattice Energy = -567.4 (Which is wrong; it should be a positive answer)

I plugged in +567.4 and it was wrong. What is going on? What does that variable V equal to in relation to my problem in the equation that you gave me from wiki?

also, it says you should subtract the electron affinity, there for making it positive in this problem. if that's the right equation you're trying to use.

mg0stisha said:
also, it says you should subtract the electron affinity, there for making it positive in this problem. if that's the right equation you're trying to use.

Ok but what is the variable "V" in my problem in relation to the equation from wikipedia:

Delta H = V + .5 B + IE - EA - U

It explains all of the variables underneath, but..

V is the enthalpy of vaporization for metal atoms.

## 1. What is Lattice Energy?

Lattice Energy is the energy released when 1 mole of a solid ionic compound is formed from its gaseous ions.

## 2. How is Lattice Energy calculated?

Lattice Energy is calculated using the Born-Haber cycle, which takes into account the formation of gaseous ions, the formation of the solid compound, and the dissociation of the solid compound into gaseous ions.

## 3. What factors affect Lattice Energy?

The factors that affect Lattice Energy include the size and charge of the ions, the distance between the ions, and the overall stability of the compound.

## 4. Why is Lattice Energy a hard question and why do I keep getting the wrong answer?

Lattice Energy can be a tricky concept to understand and calculate because it involves multiple steps and factors. It is important to carefully consider each step of the Born-Haber cycle and pay attention to the sizes and charges of the ions involved.

## 5. How does Lattice Energy relate to the stability of a compound?

The higher the Lattice Energy, the more stable the compound is. This is because a higher Lattice Energy indicates a strong attraction between the ions, making it more difficult for the compound to break apart.

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