Demonstrations for Chapter 7: Chemical Equilibrium

19. The effect of temperature on the NO₂ <=> N₂O₄ equilibrium is demonstrated. Dinitrogen tetroxide is a colorless gas and nitrogen dioxide is a deep red color. Is the reaction as written exothermic or endothermic?

20. The effect of concentration on the equilibrium involving water molecules and chloride ions coordinated with Co(II) ions in aqueous solutions is demonstrated by the shifting color of the solution as chloride ions (HCl) are added, favoring the blue CoCl₄^2- complex rather than the pink Co(H₂O)₆²⁺ complex. Write out the equilibrium reaction.

21. The effect of pH on the equilibrium between dichromate and chromate is demonstrated by adding strong acid or strong base to the solution, favoring the yellow chromate ion (CrO₄^2-) as hydroxide ion is added, or the deep orange dichromate ion (Cr₂O₇^2-) as hydronium ions are added. Write the equilibrium reaction.

22. Equilibria involving sparingly soluble salts such as silver chloride are altered by the formation of soluble complex ions. In this case, the equilibria involve formation of the soluble silver ammonia complex, a process which is reversed by addition of nitric acid: