Gen Chem Question!!!

[Mooster]

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I'm a little confused on this question from Achiever. It's number 43 in the gen chem section.

What is the concentration of O2 in equilibrium with 0.5 mol/liter of SO3 if the equilibrium constant at certain fixed temperature is 500 liter per mole?

Then they give the balanced equation

2 SO2 + O2 --> 2 SO3

Solution:

K = [SO3]^2 / [SO2]^2 [O2]^2

This makes perfect sense, but they set [O2] = y and [SO2] = 2y

Why would SO2 be 2y? I thought that the coefficient was already taken into account squaring the concentration? So basically they have 0.5^2/ (2y)^2 (y^2) but I thought it would be
0.5^2 / (y^2)(y^2)

There answer was 0.05 btw

Thanks for the help

 

[MrSummerlin]

K = [SO3]^2 / [SO2]^2 [O2]^2<-------------Wrong
K = [SO3]^2 / [SO2]^2 [O2]^1

I am not in the mood to do the problem but O2 in the solution should have a coefficient of 1. So it should be 2y and just y for o2

 

[Mooster]

Sorry I mistyped it. You're right but I'm still confused as to why it is 2y since I thought the exponent took into account the coefficient.

 

[MrSummerlin]

http://www.khanacademy.org/science/chemistry/v/reactions-in-equilibrium