A catalyst could be added to speed up the dimerization of NO2. If a catalyst is added to the syringe with 30 mL of the brown gas (which is an equilibrium mixture of NO2 and N2O4) , what change would be observed and why?

No change in color of mixture and in an equilibrium will be observed.

Explanation:

Any change in the equilibrium is studied on the basis of Le-Chatelier's principle:

This principle states that if there is any change in the variables of the reaction, the equilibrium will shift in the direction to minimize the effect.

On an addition of catalyst increases the rate of froward and backward direction,. This leads to rapid attainment of equilibrium without disturbing it. Hence, addition of catalyst will not change the equilibrium of the reaction.

So, when catalyst is added to speedup the dimerization of nitrogen dioxide( brown color) it will the equilibrium state of the reaction but it will increase the rate of forward and backward reaction. So no change in color of mixture and in an equilibrium will be observed.

indium, and thallium have three electrons i think