Qualitatively Analysing an Equilibrium

9.1 Practical Skills - Practical Skills

Select two ampoules of nitrogen dioxide gas (NO2). Place one ampoule in a beaker of warm-hot water, and one in a beaker of cold water. There will be a change in one ampoule - he one that is heated- turning reddish brown. The other will turn almost completely colourless.

The equilibrium demonstrated:

N2O4(g) ⇌ 2NO2(g)

As NO2 is a reddish brown, and N2O4 is colourless, we can effectively deduce that this equation is endothermic (Note that is the reaction was reversed such that nitrogen dioxide gas was a reactant it would exothermic).
Confirm this by stating the effects as per Le Chatelier's Principle. If the equation is endothermic, then an increase in heat should see a shift in the equilibrium towards the right, making the gas appear more reddish as more NO2 is produced. If there is a decrease in heat, then the gas would become colourless as more N2O4 is produced. The results are consistent with the hypothesis.