If I had an equilibrium of
CH3CO2(aq) + H(aq) <=> CH3CO2H(aq)
and the applied stress was HCl and NaOH what observations should I expect and what direction would the equliibrium shift?
Same goes to this question
equilibrium:Fe(aq) + SCN(aq) <=> FeSCN(aq)
the different stres applied are Fe(aq),SCN, HPO4 and Heat what observation should I expect and what direction would the equilibrium shift?
I forgot to mention that the equilbrium is 62.4 kJmol^-3 for the above quesitons
Tell us what you think and why OR tell us exactly what you don't understand about the question. We can help you best that way. I don't want to simply answer it. Le Chatelier's Principle is what you want to answer these two questions.
Well my problem is that I don't understand what exactly is the "stress" applied, and whether HCl or NaOH would be considered as catalysts?
In anycase I don't understand how do they relate to CH3CO2(aq) + H(aq) <=> CH3CO2H(aq)(as an example). I understand that when a stress is applied to a system at Equilibrium, the system readjusts. Therefore if the system readjusts then what how is it that the equilibrium will shift?
perhaps you may provide me with an example that may help me understand this better.
I wish we could write on a blackboard and I could show you with just one or two equations. But alas, such is not the case.
I'll try to walk you through but it is a lot of reading.
CH3COO^-(aq) + H^+(aq) ==> CH3COOH(aq)
First, neither HCl nor NaOH are catalysts. They are acid and base respectively and addition of an acid or base will shift the equilibrium BECAUSE the act on the H^+ that is on the left side of the equation.
Adding HCl is adding HCl ==> H^+ + Cl^- so adding H^+ forces the equilibrium to the right because that is the way to get rid of the extra H^+ that have been added; i.e., CH3COO^- reacts with the added H^+ to form more CH3COOH.
For the addition of NaOH, its just the opposite. WHY? Because NaOH is a base, the OH^- from bases react with H^+ from acids to produce water. So if we add NaOH, the OH^- reacts with the H^+ in the original equation to produce water. This actually REMOVES H^+ from the equilibrium so the reaction shifts so as to add more H^+ back to the solution. And it must shift to the left in order to add more H^+; i.e., the CH3COOH ionizes more. As to your final sentence, the system adjusts BY shifting the equilibrium. In the case of adding HCl, the CH3COOH on the right is increased and the CH3COO^- on the left is decreased. That is what we really mean when we say the system shifts to the right. I hope this helps but don't hesitate to follow up if you don't have it straight. I will leave the second question for you to work on. See if you have any problems with it.
slowly making sense.
So if I were to apply this into the equilibrium of Fe(aq) + SCN(aq) <=> FeSCN(aq)
stress applied
Fe: (aq) would shift it to the right ( I say this because I would assume that Fe is increasing and so it will shift to the right)
SCN: shift it to the right (same form of thought, increase in SCN)
HPO4: shift right (although I do not see its effect on the equation)
Heat: shift to the left
This is the equation with which we are dealing.
Fe^3(aq) + SCN^-(aq) ==> FeSCN^+2(aq)
You are correct about adding Fe^+3 and SCN^-. Addition of those ions will shift the equilibrium to the right, increasing FeSCN^+2.
HPO4^= will complex the iron and which way the reaction shift really depends upon the relative strengths of the two complexes. I couldn't find a formation constant for the phosphate complex (I found one for the SCN^- complex) but my hunch is that the iron phosphate complex is stronger and it will tie up the iron (effectively reducing it) so I think the addition of HPO4^= will shift the equilibrium to the left (but don't bet your bank account on that answer---check it out). As for the T change, where is the heat in the equation and exactly what do you mean by the equilibrium is 64.3 kJ/mol^3
The equilibrium constant (K) is not given for the reaction Fe(aq) + SCN(aq) <=> FeSCN(aq), instead, the value of 62.4 kJ/mol^-3 is given. This value represents the enthalpy change (∆H) for the reaction.
When heat is added to a reaction, it is considered a stress factor. In this case, the reaction is exothermic because the enthalpy change is negative (-62.4 kJ/mol^-3). Adding heat to an exothermic reaction will shift the equilibrium to the left, in order to absorb the excess heat.
So, the observation you can expect when heat is added to the system is that the concentration of FeSCN(aq) will decrease and the concentrations of Fe(aq) and SCN(aq) will increase.
To summarize:
1. Adding Fe(aq): This stress factor will shift the equilibrium to the right, increasing the concentration of FeSCN(aq).
2. Adding SCN(aq): This stress factor will also shift the equilibrium to the right, increasing the concentration of FeSCN(aq).
3. Adding HPO4^=: This stress factor may form a stronger complex with Fe^3+(aq) compared to SCN^-(aq), causing the equilibrium to shift to the left and decrease the concentration of FeSCN(aq).
4. Adding heat: This stress factor will shift the equilibrium to the left, decreasing the concentration of FeSCN(aq).
Remember, the role of Le Chatelier's Principle is to predict the direction in which the equilibrium will shift when stresses are applied to a system at equilibrium.