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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: positiveion on August 21, 2010, 03:38:12 AM

Title: Equilibrium Question
Post by: positiveion on August 21, 2010, 03:38:12 AM

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Title: Re: Equilibrium Question
Post by: Borek on August 21, 2010, 04:50:44 AM

Concentration of water is assumed to be constant, so it is moved into Keq value.

Title: Re: Equilibrium Question
Post by: sjb on August 21, 2010, 04:54:29 AM

BF₃ (aq) + 3 H₂O (aq)  ::equil:: 3 HF(aq) + H₃BO₃ (aq)

Keq = [HF]³ x [H₃BO₃] / [BF₃]

(please consider typing questions out, it makes the search function more efficient)

The main reason that water is not considered in this instance is because it's the solvent, any changes in its concentration as a result of the reaction will be very small, effectively a constant in this case. If the reaction were much more concentrated then it would probably be best to include it as well.

Title: Re: Equilibrium Question
Post by: dkasprick on August 25, 2010, 04:35:57 AM

Isnt it because pure solids and pure liquids arent included in equilibrium  constant expressions ?

Title: Re: Equilibrium Question
Post by: Borek on August 25, 2010, 06:18:59 AM

No, that holds when they are in separate phases.