chemistry
posted by Jessica .
A researcher put 10.0 moles of N2O into a 2L container at some temperature where it decomposes according to the following: N2O = 2N2+ O2. At equilibrium 2.20 moles of N2O remain. Calculate the Kc for the reaction.

You didn't balance the equation.
Set up an ICE chart. (N2O) initially = 10.0moles/2L = 5M
............2N2O ==> 2N2 + O2
initial.....10.0M....0......0
change.......x......+2x...+x
equilibrium..10.00x..2x....x
Kc = (N2)^2(O2)/(N2O)^2
You are given that at equilibrium the N2O is 2.20 moles.
10.00x = 2.20, solve for x and complete the table. Convert moles to M in all cases and substitute into Kc expression and solve for Kc. 
Kc = 24.5