Calculating fraction of aluminum lttice sites at certain temps

[SBloodshield]

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 without 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?

 

[Navin A S]

Nexp is the number of atoms in the lattice that can form a vacancy. It is equal to the product of the density of the lattice, N, and the probability of an atom forming a vacancy, exp(-E_v/kT). K is Boltzmann's constant, which is a physical constant with a value of 8.62x10^-5 eV/K.