# Finding the composition of a mixture at equlibrium

1. Oct 15, 2008

### minute34

1. The problem statement, all variables and given/known data

Initially a mixture contains 0.723 mol each of N2 and O2 in an 7.20 L vessel. Find the composition of the mixture when equilibrium is reached at 3900°C. For the reaction below, the Kc = 0.0123 at 3900°C.
N2(g) + O2(g) 2 NO(g)

2. Relevant equations
I.C.E Tables (not an equation but relevant) and the quadtratic formula

x=-b +or- sq root(b^2 -4ac) / 2a

3. The attempt at a solution

I did my I.C.E Table
Conc.(M) N2 + O2 --> 2 NO
Start 0.6025 0.6025 0
Change -x -x 2x
Eq. 0.6025-x 0.6025-x 2x

Then I plugged that into my Kc formula
Kc=[products]/[reactants]
0.0123=[2x]^2/[0.6025-x][0.6025-x]

I then rearranged that to get a quadratic equation to solve for x (this is where I think I made a mistake)
-324x^2 -1.205x +0.3630=0
I plugged it into the quadratic formula and
got 0.03166 for x, which i plugged into the equations from the EQ. line in my I.C.E table, however when i plugged those values into the Kc formula, i didn't come out with the Kc value I was given (0.0123)

Can anyone help?

2. Oct 15, 2008

### minute34

nevermind, I was (stupidly) using a value from another question, but my method was right.