Chemistry
posted by Hannah .
For the reaction system, 2 H2O(g) + O2(g) == 2 H2O2 (g), the equilibrium concentrations are
(H2O2) = 0.120 M; (H2O) = 0.860 M; (O2) = 0.330 M.
Calculate the value of Kc for this reaction.
A. 0.423
B. 0.872
C. 0.0590
D. 1.31
E. 2.51
I did 0.120 / 0.860 X 0.330 = 4.4228 = 4.23.
Did I do this correctly?

You didn't balance the equation and you didn't make the coefficients the exponents.

To balance the equation would I add a 2 in front of the O2?

To know if it balances or not, count the atoms and see. You don't need to ask anyone. You want to put a 2 for O2?
2H2O + 2O2 ==> H2O2.
I see 4 H atoms on the left. I see 2 on the right. Equation isn't balanced. 
so then 4.

2H2O + 4O2 ==> H2O2
I see 4 H atoms on the left and 2 on the right. Equation isn't balanced. Quit guessing and count the atoms. Try a value and count. It's that simple.