Knowledge database: Chemical reactions: Association and dissociation

Reactions of association and dissociation are reactions in which particles, depending on the conditions, change from one structural form to another. Thereby, these particles can be either atoms, molecules or ions.

One of the most well known cases is the change of the form of nitrogen dioxide, shown by the following formula: 2NO₂ <-> N₂O₄.

This change is shown on the picture above. Nitrogen dioxide is placed in a glass bulb. On the picture to the left, the bulb is placed in cold water, and thereby there is more product (N₂O₄) in the bulb, which is colorless, and because of that, the color of the gas is lighter. On the picture to the right, the bulb is placed in hot water, and now there is a larger amount of the reactant (NO₂) which is dark brown colored, and because of that, one can notice a darker color of the gas in the glass bulb.