Nitrogen dioxide equilibrium. Nitrogen dioxide (NO2) gas exists in equilibrium with dinitrogen tetroxide (N2O4) gas, 2NO2 N2O4. Two sealed ampoules with nitrogen dioxide are placed in beakers with hot water (left) and ice water (right). According to Le Chatelier's principle higher temperature shifts the equilibrium to nitrogen dioxide (brown colour) while lower temperature shifts the equilibrium to dinitrogen tetroxide (colorless).