Concentrations.... ?

Question

chem 2 question .

we place 1.32 mol PCl5 in a 1.0 L flask and allow it to reach equillibrium ata given temp. What it the final concentration of Cl2 in the Flask.

PCl5--> PCl3+Cl2

Kc= .47

The answer is 0.59 M

but how do you get it?

Answer 1

Kc = [PCl3][Cl2] / [PCl5]
let x equal the moles of PCl3 (and of Cl2) at equilibrium
0.47 = [x][x] / [1.32-x]
(0.47)(1.32)-0.47x = x^2
x^2 + 0.47x -0.6204=0
x=0.59

Answer 2

The equation you need to solve is (x squared)/(1.32 - x) = 0.47.

x is the molarity of PCl3 and also Cl2.