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Does [H3O+][OH-] always equal 10^-14?

Posted: Tue Jan 22, 2019 9:27 pm
by Michelle Song 1G
Under what conditions does it not equal 10^-14? For 6B.9 [H3O+][OH-] does not equal 10^-14...

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Tue Jan 22, 2019 9:38 pm
by Jeannine 1I
I'm not sure what that problem is since I have the 6th edition, but I believe it is 10^-14 under lab conditions, which means the temperature is constant. Even then, I'm not sure if it is ALWAYS equal to 10^-14. I'd like to know too, it's a good question!

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Tue Jan 22, 2019 9:38 pm
by Katie Sy 1L
it is 10^-14 only when water is at a constant 25 degrees C

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Tue Jan 22, 2019 9:43 pm
by marisaimbroane1J
For the purpose of this class, I think the reactions we will be given will all be at 25 degrees Celsius if we are expected to use Kw. As long as the temperature is 25 Celsius, Kw=10^-14.

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Tue Jan 22, 2019 9:47 pm
by Max Hayama 4K
Kw will be 10^-14 only if the temperature is 25 degrees Celsius. If the temperature is different, the equilibrium constant for the autoprotolysis of water will also be different. This is because autoionization is endothermic, meaning an increase in temperature will result in more products, shifting equilibrium to the right.

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Wed Jan 23, 2019 9:47 am
by Ricardo Martin 1J
It is only equal to 10^-14 when water is at 25 degrees C. However, I believe (at least so far) our reactions will be given in this condition.

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Wed Jan 23, 2019 2:18 pm
by Angela Cong 3C
even if kw is not equal to 1*10^-14, [H3O+][OH-] is still equal to kw and to find concentration, you just sqaureroot the kw

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Wed Jan 23, 2019 2:49 pm
by 2c_britneyly
Any time there is a change in temperature then Kw is subject to change. For the purpose of this class we assume Kw=10^-14

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Wed Jan 23, 2019 3:32 pm
by Tony Chung 2I
Yes, only if the temperature of the water is at a constant temperature of 25 degrees celsius.

Re: Does [H3O+][OH-] always equal 10^-14?

Posted: Thu Jan 24, 2019 9:53 pm
by abbydouglas1K
Michelle Song 1G wrote:Under what conditions does it not equal 10^-14? For 6B.9 [H3O+][OH-] does not equal 10^-14...

I ran into this same problem and I am not 100% sure why it does not work because it works for the last two parts but it may be because we can not assume that the values of the temperature are constant.