MODEL RELEASED. Chemical equilibrium experiment. Image 1 of 2. Student holding a sealed syringe full of a mixture of nitrogen dioxide (NO2, a brown gas) and dinitrogen tetroxide (N2O4, a colourless liquid). These chemicals exist in a dissociative equilibrium, with two molecules of NO2 combining to form a molecule of N2O4, and vice versa. Changes in temperature and pressure change the equilibrium. Here, the student is about to apply pressure, forcing the equilibrium to the N2O4 side (as that has fewer molecules and less pressure), reducing the amount of NO2 and reducing the brown colour. See image H460/484 for the result.