[phys]

QUESTION:
K=1.6 X 10^-5 for the reaction

2 NOCl  2 NO + Cl₂

If 2.0 mol NO and 1.0 mol Cl₂ are placed into a 1.0L flask, calculate the equilibrium concentration of NO.

Attempt:
Since the question being asked is for the reverse of this reaction, the value of K=62500 correct? Since K_f=1/K_r?
I set up an ICE table, but I can't seem to solve for x:

    2NO    Cl₂    2NOCl
I    2.0     1.0    0.0
C   -2x     -x     +2x
E  2.0-2x  1.0-x  2x

K= [NOCl]²
    [NO]²[Cl₂]

Have I got this all set up and right? If or if not, how do I solve for x? When I substitute the equations from the ICE table into the equilibrium constant equation and expand/simplify, I end up with an x³ that I can't use the Quadratic Formula to solve.

[Jorriss]

A couple things. Can you use a calculator? If so, cubic roots are easy, if not, you'll need to do some approximations (there are methods for determining zeros but I doubt you are required to do those).


Secondly, your reaction doesn't correspond with your K expression. Either your K needs to be written as its reciprocal or your reaction is backwards.