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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: cvc121 on April 18, 2015, 04:01:21 PM

Title: Le Chatelier's Principle
Post by: cvc121 on April 18, 2015, 04:01:21 PM

Hi,

For the reaction CoCl4^2-(aq) + 6H2O(l)  :resonance: Co(H2O)6²⁺(aq) + 4Cl^-(aq) + heat, how does adding KCl, adding AgNO3 which reacts with Cl^-, and adding water affect the goal, shift, [CoCl4^2-], H2O, [Co(H2O)6²⁺], [Cl^-], and heat.

Here is my attempt:
I am not sure about this but is KCl a catalyst? If so, I would say that it has no effect on anything (it just increases the rate at which the system reaches equilibrium). What would the goal be though?

For adding AgNO3, would it decrease the concentration of [Cl^-]? How would it affect the others? What is the goal and the shift? Really confused about this one.

For H2O, decrease [] of the aqueous substances because it causes there to be more solvent. However, how would you know what way the reaction would shift? And how does the shift affect the [] of the substances? Also, would the goal be to decrease H2O?

Title: Re: Le Chatelier's Principle
Post by: Borek on April 18, 2015, 05:36:21 PM

Adding KCl means adding Cl^-, adding AgNO₃ means removing Cl^-. Le Chatelier's principle tells you the system will try to counter the effect.

You have water on the left - you add water. Same kind of a problem.

Title: Re: Le Chatelier's Principle
Post by: cvc121 on April 18, 2015, 09:15:23 PM

Makes sense. Greatly appreciate the help, Borek. I just have a couple more quick questions. If the stress is adding KCl for example, would the goal be to decrease [KCl] or [Cl^-]? Also, if you add water to the reaction NaOH(s)  :resonance: Na⁺(aq) + OH^-(aq), the aqueous substances would all decrease in concentration because there is more solvent, right? So the reaction would shift to the right because the goal is to increase the [Na⁺] and [OH^-] right?

Title: Re: Le Chatelier's Principle
Post by: Borek on April 19, 2015, 03:58:08 AM

Quote from: cvc121 on April 18, 2015, 09:15:23 PM

If the stress is adding KCl for example, would the goal be to decrease [KCl] or [Cl^-]?

Why decrease, if you add? In general - question as asked is impossible to answer. If you add diluted KCl solution you can be diluting both KCl and Cl^- (and K⁺). If you add a solid KCl typically it will mean increasing [KCl] and [Cl^-]. In general I would prefer to think in terms of K⁺ and Cl^- separately, as in most cases one of them will be most likely a spectator.

Quote

Also, if you add water to the reaction NaOH(s)  :resonance: Na⁺(aq) + OH^-(aq), the aqueous substances would all decrease in concentration because there is more solvent, right? So the reaction would shift to the right because the goal is to increase the [Na⁺] and [OH^-] right?

Reaction will definitely shift right, whether it is "the goal" - and of what - I can not say.