Excluding H2O from Ka and Kb

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J Medina 2I
Posts: 102
Joined: Wed Sep 25, 2019 12:17 am

Excluding H2O from Ka and Kb

Postby J Medina 2I » Sat Jan 25, 2020 6:44 pm

I know we don't include H2O (l) in caluclations for Kb and Ka but why is that?

Elena Bell 1C
Posts: 64
Joined: Thu Jul 11, 2019 12:16 am

Re: Excluding H2O from Ka and Kb

Postby Elena Bell 1C » Sat Jan 25, 2020 6:46 pm

H2O is typically used as a solvent in its liquid form, so the concentration does not change much before and after the reaction occurs. Since it mostly stays the same, it would not have an affect on the rate of the reaction.

Kayla Maldonado 1C
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Re: Excluding H2O from Ka and Kb

Postby Kayla Maldonado 1C » Sat Jan 25, 2020 6:49 pm

Water is a pure liquid and has an activity equal to 1, therefore, it does not affect the equilibrium constant.

Anika Chakrabarti 1A
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Joined: Sat Aug 24, 2019 12:17 am

Re: Excluding H2O from Ka and Kb

Postby Anika Chakrabarti 1A » Sat Jan 25, 2020 6:57 pm

When H2O is a solvent it is in so much excess that its concentration doesn't change.

rabiasumar2E
Posts: 108
Joined: Thu Jul 11, 2019 12:15 am

Re: Excluding H2O from Ka and Kb

Postby rabiasumar2E » Sat Jan 25, 2020 7:14 pm

Solids and liquids don't affect the value of K, therefore we don't include them in the calculations!

Max Madrzyk Dis 4G
Posts: 102
Joined: Wed Sep 18, 2019 12:21 am

Re: Excluding H2O from Ka and Kb

Postby Max Madrzyk Dis 4G » Sat Jan 25, 2020 7:16 pm

We don't include H2O (l) in our calculations of Ka and Kb because water is going to be present in so much excess in both the reactants and the products that if we plugged it into the equation the two numbers would just cancel each other out.


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