# Homework Help: Where Did I Mess Up In Solving This?

1. Apr 25, 2013

### JeweliaHeart

1. The problem statement, all variables and given/known data
For the reaction: A + B ↔ C + D

6.0 moles of A and 5.0 moles of B are mixed together in a suitable container. When equilibrium is reached, 4.0 moles of C are produced.

The equilibrium constant for this reaction is:

a. K = 1/8
b. K = 8
c. K = 30/16
d. K = 16/30

2. Relevant equations

K=[C][D]/[A]

3. The attempt at a solution

I set up the problem like this:

Initial Concentrations: [A] 6/x 5/x [C] 0 [D] 0

Change in Concentrations: [A] -4/x -4/x [C] +4/x [D] 0

Equlibirum Concentrations: [A] 2/x 1/x [C] 4/x [D] 0

I assigned the variables x myself:
x= volume of container

The reason I put 0 for D's concentration is b/c the problem did not say any amount of D was formed.

Therefore the equilibrium expression should look like this:
[4/x]/[2/x^2]
which further equates to 2x. I don't where I messed up or how to solve this. Any help would be appreciated. Thanks.

2. Apr 25, 2013

### Infrared

Well if 4 moles of C are produced, how many moles of D are produced? Also, if if it were 0, then you would find that the equilibrium constant is zero by the formula for K and you could not just ignore it.

3. Apr 25, 2013

### JeweliaHeart

oh....duh *hits forhead*. Thanks so much. How silly of me to overlook that.