Posted by Mary on .
In a solution of copper(II) chloride, the following equilibrium exists:
CuCl42-(aq) (dark green) + 4H2O(l) <--> Cu(H2O)42+(aq)(blue) +4 Cl-(aq)
Predict the shift in the equilibrium and draw a graph of concentration versus time for relevant reactants to communicate the shift after the following stresses are applied to the system:
(a) HCL acid is added
(b) Silver nitrate is added.
It is impossible to draw diagrams on the board to show you how this works and words sometimes fail to communicate properly; however, remember Le Chatelier's Principle. A reaction at equilibrium will try to UNDO what we do to it (although Le Chatelier's statement was much more esoteric). Therefore, it we add HCl (we are adding Cl^-), the reaction will shift so as to undo what we did. Since we added Cl^-, the reaction will shirt to try to get rid of Cl^-; ie., use it up. If it shift to the right, more Cl^- is formed so it won't do that. Shifting to the left uses Cl^- and that is what it will do.
Add AgNO3 and you know Ag^+ will react with Cl^- to produce insoluble AgCl
Ag^+(aq) + Cl^-(aq) ==> AgCl(s)
So we are removing Cl^- from the reaction to form solid AgCl. The reaction will shift so as to undo what we did. Since Cl^- is being removed, the reaction will shift to produce more Cl^- which means it will shift to the right.