Calculating fraction of aluminum lattice sites at temps

[SilverBloodshield]

Calculating fraction of aluminum lttice sites at certain temps
So do to a few issues I have definitely missed some thing in my materials class so I hope I'm not going to be told I'm an idiot. Please forgive me if I seem dense I am a single mother with a one year old who is also tackling an engineering degree ^_^'''

So with out further ado... I am working on this problem
"Calculate the fraction of Aluminum lattice sites vacant at a) 500 C b)200 C
and c) Room temp assumed at 25 C given that the energy to form a vacancy om aluminum is 0.76 ev/atom."

Ok I am assuming I am using some vartion of this equation Nv=nexp(-q/KT)

My question is what is nexp? I never quite catch what that was supposed to represent.

and I also think I missed something else in my note because I have an example problem in them where for it the energy for vacancy is listed as .9 ev/atom but I have K written as 8.62x10 to the -5 ev/atom is K a constant I should just have memorized?

[VorpalNeko]

Sounds like you're asked to use an Arrhenius equation to get the fraction of vacancies Nv to total lattice sites n: Nv/n = exp(-q/kT). The q/k = (0.76eV)/k = 8820K is the same throughout the problem.
P.S. Don't confuse K (kelvin) with k = k_B (Boltzmann constant) = 8.6173324E-5 eV/K.

[SilverBloodshield]

Thank you for clearly explaining it that helps a lot! I had definitely been heading the wrong direction there is a second exultation that has an r instead of the k and I was trying to use that X.x suffice to say it was not working