How Do You Calculate Equilibrium Partial Pressures in a Chemical Reaction?

[Xels]

Homework Statement

At 600 K the equilibrium constant is 38.6 for the reaction

2 HI(g) <--> H2(g) + I2(g)

Start with a pressure of 0.725 atm consisting of only HI(g) at 600 K. Calculate the equilibrium
partial pressures of HI, H2 and I2.

Homework Equations

K=[C]^n[D]^n/[A]^n
Qp = 0 (shift to the right)
ax^2+bx+c
x=((-b+/-((b^2-4ac)^(1/2)))/(2a))

The Attempt at a Solution

Given the gas state atm is treated as mol

2HI H2 I2
I .725 0 0
C -2x x x
E .725-x x x

38.6 = (x*x)/(.725-x)^2
38.6 = (x*x)/(x^2-1.45x+.526)
x^2-1.45x-38.074 = 0

x=((1.45+/-((1.45^2-4*1*38.074)^(1/2)))/(2*1))
+x= 5.48
-x = -6.94 (discounted)

I'm either doing it totally wrong or I'm clueless as to where to go from here. I'm assuming I need to find the final pressure of x and then calculate partial pressure using Pa/Pt etc.

 

[Borek]

C -2x x x
E .725-x x x

Some inconsistency here...

And I have not checked details, but solving

38.6 = (x*x)/(.725-x)^2

doesn't yield

+x= 5.48
-x = -6.94

 

[Xels]

I got +/- x by solving (x*x)/(.725-x)^2 quadratically. I'm not sure where to go past this to find partial pressures.

 

[Xels]

After much reworking I found my error. Thanks for your input Borek.