We place 6.7 mol pcl5 in a 1.0 l flask and allow it to reach equilibrium at a given temperature. what is the final concentration of cl2 in the flask?

WE are given 6.7 moles of PCl₅ in a 1 liter flask. And we are to find the final concentration of Cl₂. Before we can get to it, we have to find the reaction that produces Cl₂.

PCl₅ → Cl₂ + PCl₃

Since the reaction produces equal moles of Cl₂ and PCl₃, then Cl₂ is also equal to 6.7 moles. 

Molarity = number of moles of solute/liter of solution
Molarity of PCl₅ = 6.7/1 = 6.7 molarity of Cl₂

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic