I feel like I know what I'm doing but I'm not getting an answer that is offered. Heres the question:(adsbygoogle = window.adsbygoogle || []).push({});

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?

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# Homework Help: Chemistry - calculating equilibrium constant, what am I doing wrong?

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