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.
(a) When HCl acid is added to the system, it will increase the concentration of Cl- ions. According to Le Chatelier's principle, the system will shift in a direction that opposes the change. In this case, that means the equilibrium will shift to the left to decrease the concentration of Cl- ions.
As a result, the concentration of CuCl42- (dark green) will increase, and the concentration of Cu(H2O)42+ (blue) will decrease.
Graph of concentration versus time for relevant reactants:
[Graph]
The graph will show an increase in the concentration of CuCl42- (dark green) and a decrease in the concentration of Cu(H2O)42+ (blue) over time due to the shift in equilibrium towards the left.
(b) When silver nitrate is added to the system, it will increase the concentration of Ag+ ions. Applying Le Chatelier's principle, the equilibrium will shift in a direction that reduces the concentration of Ag+ ions. In this case, that means the equilibrium will shift to the right to decrease the concentration of Ag+ ions.
As a result, the concentration of Cu(H2O)42+ (blue) will increase, and the concentration of CuCl42- (dark green) will decrease.
Graph of concentration versus time for relevant reactants:
[Graph]
The graph will show an increase in the concentration of Cu(H2O)42+ (blue) and a decrease in the concentration of CuCl42- (dark green) over time due to the shift in equilibrium towards the right.
To predict the shift in the equilibrium and draw a graph of concentration versus time for the relevant reactants, we need to consider Le Chatelier's principle. According to this principle, when a system at equilibrium is subjected to a stress, the system will shift to counteract the effect of the stress and restore equilibrium.
(a) When HCl acid is added to the system, it introduces additional chloride ions (Cl-) to the solution. Since the reaction already involves Cl- ions on the reactant side, adding more Cl- ions will shift the equilibrium toward the product side (to the right) to counteract the increase in chloride ions. This means more Cu(H2O)42+ (blue) will form.
(b) When silver nitrate (AgNO3) is added to the system, it introduces additional silver ions (Ag+) to the solution. The presence of Ag+ ions will react with chloride ions (Cl-) to form a precipitate of silver chloride (AgCl), which reduces the concentration of Cl- ions in the solution. To counteract this decrease in Cl- ions, the equilibrium will shift to the left, favoring the reactant side, to produce more CuCl42- (dark green).
Now, let's draw a graph to visualize the changes in concentration over time for the relevant reactants:
For part (a):
- The concentration of CuCl42-(aq) (dark green) will decrease over time since the reaction shifts to the right to form more Cu(H2O)42+(aq) (blue).
- The concentration of Cu(H2O)42+(aq) (blue) will increase over time as more is formed.
Graph for part (a):
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Time
For part (b):
- The concentration of CuCl42-(aq) (dark green) will increase over time since the reaction shifts to the left to form more CuCl42- (dark green).
- The concentration of Cu(H2O)42+(aq) (blue) will decrease over time as it reacts with additional Cl- ions.
Graph for part (b):
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Time
Please note that the concentrations and rate of change depicted in the graph are for illustrative purposes only and may not necessarily reflect the actual values. The actual values will depend on the specific reaction conditions and concentrations used.