Kw= [H30+]*[OH-]

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Andy Nguyen 1A
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Joined: Thu Jul 27, 2017 3:00 am

Kw= [H30+]*[OH-]

Postby Andy Nguyen 1A » Fri Dec 01, 2017 4:36 pm

In lecture today we found the equation for kw, which was Kw= [H30+]*[OH-], from the chemical reaction 2H20 --> H30+ + OH-. Is H2O not part of the equation for Kw because it is in a liquid state? Dr. Lavelle also mentioned that it was because there was a large amount of water but I'm not sure what he meant by that. Thank you in advance!

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Re: Kw= [H30+]*[OH-]

Postby RaviAmin1H » Fri Dec 01, 2017 5:13 pm

Acids and bases ionize in water. So both are aqueous. The reaction takes place in water, so it is not a limited concentration.

Miranda 1J
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Re: Kw= [H30+]*[OH-]

Postby Miranda 1J » Fri Dec 01, 2017 5:18 pm

I think what Dr. Lavelle meant by the water being in large excess was that so little of it is ionized at any one time, that its concentration remains virtually unchanged, so essentially just another constant in the equation.

Michelle Steinberg2J
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Re: Kw= [H30+]*[OH-]

Postby Michelle Steinberg2J » Mon Dec 04, 2017 3:58 pm

Similar to how we do not include solvents in the equilibrium constant "K" , we do not consider the solvents in Kw either. We consider the concentration unchanged, so we omit H20.

Suhail Zaveri
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Joined: Sat Jul 22, 2017 3:01 am

Re: Kw= [H30+]*[OH-]

Postby Suhail Zaveri » Mon Dec 04, 2017 4:02 pm

Dear student,

I don’t think water is counted because it is a solvent and a liquid. Usually in a equilibrium equation liquids and solids are omitted. Only aqueous compounds can be used in the K for equilibrium. Therefore only the ions h3o plus and OH- are included.

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