How Does Adding Hydrochloric Acid or Silver Nitrate Affect Chemical Equilibrium?

[erik05]

Hello there. I'm having trouble understanding equilibrium. Especially understanding if the reactions go foward or reverse when there is a change in tempertature, concentration, pressure/volume etc. For example:

In a solution of copper (II) chloride, the following equilibrium exists.

CuCl_4^{2-}_{(aq)} + 4H_2O_{(l)} \rightleftharpoons Cu(H_2O)_4^{2+}_{(aq)} + 4Cl^{-}_{(aq)}

For the following stresses put on the equilirbrium, predict the shift in the equilibrium.

1) Hydrochloric acid is added
2) Silver nitrate is added.


1) Would this be a reverse reaction since the acid dissociates into HCl_{(aq)} \rightarrow H^{+}_{(aq)} + Cl^{-}_{(aq)}? So the concentration of Cl will be increased and it will shift to the left?

2)I think it's a reverse reaction but I'm not sure. Why would it be a reverse reaction (or foward if I'm wrong)? Thanks for the help.

 

[MathStudent]

Hello there. I'm having trouble understanding equilibrium. Especially understanding if the reactions go foward or reverse when there is a change in tempertature, concentration, pressure/volume etc. For example:

In a solution of copper (II) chloride, the following equilibrium exists.

CuCl_4^{2-}_{(aq)} + 4H_2O_{(l)} \rightleftharpoons Cu(H_2O)_4^{2+}_{(aq)} + 4Cl^{-}_{(aq)}

For the following stresses put on the equilirbrium, predict the shift in the equilibrium.

1) Hydrochloric acid is added
2) Silver nitrate is added.


1) Would this be a reverse reaction since the acid dissociates into HCl_{(aq)} \rightarrow H^{+}_{(aq)} + Cl^{-}_{(aq)}? So the concentration of Cl will be increased and it will shift to the left?

Yes exactly,

2)I think it's a reverse reaction but I'm not sure. Why would it be a reverse reaction (or foward if I'm wrong)? Thanks for the help.

Silver nitrate is soluble in water, but silver chloride isn't. So adding silver nitrate is like taking away chloride ions from solution...

 

[thepatientmental]

Hello! Understanding equilibrium can definitely be tricky, but I'm happy to help clarify things for you.

First, let's review what equilibrium means. In a chemical reaction, equilibrium is reached when the rate of the forward reaction is equal to the rate of the reverse reaction. This means that the amounts of reactants and products in the reaction remain constant over time, even though the reaction is still occurring.

Now, let's look at the stresses you mentioned and how they would affect the equilibrium in the given reaction:

1) When hydrochloric acid is added, it will dissociate into H+ and Cl- ions. This means that the concentration of Cl- ions will increase, as you mentioned. According to Le Chatelier's principle, when a stress is applied to an equilibrium, the equilibrium will shift in a way that minimizes the effect of the stress. In this case, the increased concentration of Cl- ions will cause the equilibrium to shift to the left, towards the reactants, in order to reduce the excess Cl- ions. So, you are correct that this would be a reverse reaction.

2) Similarly, when silver nitrate is added, it will dissociate into Ag+ and NO3- ions. This will increase the concentration of Ag+ ions, causing the equilibrium to shift to the left in order to reduce the excess Ag+ ions. So, this would also be a reverse reaction.

In both cases, the equilibrium shifts to the left because the forward reaction is exothermic (releases heat), and by shifting to the left, it can consume some of the excess ions and release heat to balance out the added stress.

I hope this helps clarify things for you. Remember, when in doubt, always think about how the equilibrium would shift to minimize the effect of the stress. Good luck with your studies!