Lattice Energy confusion

[MrNeuro]

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So after doing some lattice energy/heat of hydration?heat of solution problems I've come to realize that different texts contradict each other and refer to lattice energy as exact opposites.
Wiki sort of elucidates this. (right below the reaction mechanism)

Where they note that some "older" textbooks refer to
Lattice energy as the energy required to convert the ionic compound into its gaseous ions hence yielding an ENDOTHERMIC process.

However according to wiki they say lattice energy is the energy of formation, or in parallel to what was noted above, the energy required to convert gaseous ions into a solid hence yielding an EXOTHERMIC process.

So i guess my question is what convention do i follow?

Do i just use the sign convention where if its negative it must be gas to solid and if its positive it must be solid to gas?

What about energy of crystallization is that always going to be gas to solid or will it be the opposite of whatever the text refers to as the energy of crystallization?

Thanks

 

[gettheleadout]

As I learned it (which I will assume is the current convention) lattice energy refers to the enthalpy change of the formation of ionic solid from gaseous ions, and should be negative (exothermic).

 

[MrNeuro]

As I learned it (which I will assume is the current convention) lattice energy refers to the enthalpy change of the formation of ionic solid from gaseous ions, and should be negative (exothermic).

so then crystallization is positive (endothermic) enthalpy change of gas from solid?

 

[chiddler]

Breaking bonds is endothermic. Forming bonds is exothermic.

Why is lattice energy different if it is breaking bonds?

 

[gettheleadout]

so then crystallization is positive (endothermic) enthalpy change of gas from solid?

If you're referring to ionic solid -> gaseous ions then yes, deltaH is positive and the change is endothermic.

Chiddler, no bonds are being broken but an ionic bond is being formed between the free gaseous ions, thus exothermic lattice energy.

 

[chiddler]

oh. I went opposite way.

thanks.