At some point, the reaction reaches equilibrium, where the rates of forward and reverse reactions are equal. The concentrations of NO2 and N2O4 no longer change.

[NO2] = 0.50 M [N2O4] = 1.50 M

The reaction quotient (Q) is calculated as:

The reaction quotient (Q) becomes:

Q = [N2O4] / [NO2]^2 = 1.00 / (1.00)^2 = 1.00

Suppose we add 1.00 M of N2O4 to the container. The new concentrations are:

Q = [N2O4] / [NO2]^2 = 1.33 / (0.67)^2 = 2.96

The reaction still is not at equilibrium.