The nitrogen dioxide - dinitrogen tetroxide equilibrium

In this experiment we investigate the equilibrium between colourless dinitrogen tetroxide and brown nitrogen dioxide gases represented by the following equation:

N₂O₄(g)2NO₂(g)

The video shows the production of nitrogen dioxide gas by the thermal decomposition of solid lead nitrate. Care has to be taken in this experiment as lead nitrate is toxic and is a cumulative poison. Nitrogen dioxide gas is also highly poisonous, and so the experiment must be performed in a fume cupboard. We want to see what effect changes in pressure and temperature have on the above equilibrium. You may wish to review Le Chatelier's principle at this point. You will need to know that this reaction is endothermic (remember we always quote the value for the left to right reaction).

Watch the video carefully, and make a note of what happens to the depth of the brown colour when the equilibrium mixture is heated and cooled. Remember, the darker the brown, the more nitrogen dioxide gas there is. The final sequence of video shows the pressure on the equilibrium mixture being suddenly released. Observe very carefully the colour changes that occur after the pressure is released. You will need some skill here, as they are not easy to see. The reverse happens when the pressure is increased, but this has not been shown on the video. Try to explain the changes you observe by using Le Chatelier's principle. You can check your answer on the link below.

Video - the dinitrogen tetroxide and nitrogen dioxide equilibrium

Explanation in terms of Le Chatelier's principle