I feel like I know what I'm doing but I'm not getting an answer that is offered. Heres the question: Dinitrogentetraoxide partially decomposes according to the following equilibrium: N2O4 (g) ---> 2NO2 (g) (an arrow going other way too) A 1.00-L flask is charged with .400 mol of N2O4. At equilibrium at 373 K, 0.0055 mol of N2O4 remains. Equil. constant for this reaction is __________. a. 2.2 x 10^-4 b. 13 c. 0.22 d. 0.022 e. 0.87 K = [NO2]^2 / [N204] N2O4 goes from .4 to .0055 mol, so that is a change of .3945 mol, which must be the equilibrium amount of the 2NO2. Since the volume is just 1 L K = [.3945 M]^2 / [.0055 M] = 28.3 but this is not one of the choices. what am I doing wrong?