# Question #b2b2b

##### 2 Answers

This is a very simple problem if you're familiar with the **Born-Lande equation** for calculating lattice energies. Here's how that looks like

I won't list what all the terms in this equation mean because all but three of them are not important. The three terms that you should focus on are

Now, I believe that you are supposed to ignore the terms that are specific to individual ionic compounds, and assume that all the constants for your hypothetical salt are identical to those for

If that's the case, you can rewrite the above equation like this

Now, because

In the case of **+1** and **-1**; you can use this to write the lattice energy of

Since **+2** and **-2**, you'll get

Rounded to three sig figs, the answer will be

The lattice energy of

If we consider 2 charges

So

We can find the work done in separating these charges from a distance

From which we get:

This means that if we double the charges the work done required to separate them would go up by 2 x 2 = 4.

This means that in your example the lattice energy would increase to 4 x -744 =

In this answer I have only considered 2 charges separated by a distance

A more accurate expression for lattice enthalpy

I won't go further into the details of this. If you want you can look up "Madelung Constant".