Why is K unitless?

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Ellis Song 4I
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Joined: Thu Jul 11, 2019 12:17 am

Why is K unitless?

Postby Ellis Song 4I » Thu Jan 09, 2020 4:02 pm

Why does the equilibrium constant, K, not have units?

Abhi Vempati 2H
Posts: 104
Joined: Fri Aug 09, 2019 12:17 am

Re: Why is K unitless?

Postby Abhi Vempati 2H » Thu Jan 09, 2020 4:04 pm

We use reactivity to calculate K, and concentrations/partial pressures are just an approximation of the reactivities. Reactivities have no units, so K will therefore not have any units. This was covered in the modules and lectures in further detail. Hope this helps!

KnarGeghamyan1B
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Joined: Fri Aug 09, 2019 12:15 am

Re: Why is K unitless?

Postby KnarGeghamyan1B » Thu Jan 09, 2020 4:33 pm

When we set up the equation for K, it is K= [M]/[M], as in a concentration over another concentration. So just think of it as canceling out the units M in the fraction, leaving you with a unitless number.

Tai Metzger 3K
Posts: 103
Joined: Sat Aug 24, 2019 12:17 am

Re: Why is K unitless?

Postby Tai Metzger 3K » Thu Jan 09, 2020 4:39 pm

K is essentially a ratio (between products and reactants) and so it does not have units.

annikaying
Posts: 94
Joined: Sat Sep 14, 2019 12:16 am

Re: Why is K unitless?

Postby annikaying » Thu Jan 09, 2020 4:48 pm

K is a ratio and therefore is moreso a comparison than a value. You can also think of the units as canceling as the units on top equal that of the bottom.

Jocelyn Thorp 1A
Posts: 103
Joined: Wed Sep 18, 2019 12:20 am

Re: Why is K unitless?

Postby Jocelyn Thorp 1A » Thu Jan 09, 2020 5:20 pm

it's just a constant representing the ratio of the concentrations. Looking at the units, they would cancel each other out :)

Diana Andrade_4F
Posts: 50
Joined: Tue Nov 05, 2019 12:18 am

Re: Why is K unitless?

Postby Diana Andrade_4F » Thu Jan 09, 2020 7:53 pm

K is just a ratio of products/reactants, so there are no units. Also, when calculating K, the units just cancel out.

Megan Kirschner
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Joined: Wed Feb 20, 2019 12:17 am

Re: Why is K unitless?

Postby Megan Kirschner » Thu Jan 09, 2020 7:59 pm

K is y a ratio (between products and reactants) and so it does not have units- but so does this mean that all ratios we use in this class will be unitless? Is it safe to apply this rule widely?

Jocelyn Thorp 1A
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Joined: Wed Sep 18, 2019 12:20 am

Re: Why is K unitless?

Postby Jocelyn Thorp 1A » Sun Jan 19, 2020 4:12 pm

Megan Kirschner wrote:K is y a ratio (between products and reactants) and so it does not have units- but so does this mean that all ratios we use in this class will be unitless? Is it safe to apply this rule widely?


If it's simply a ratio then most likely, yes. Constants will come with their units but ratios should remain unitless.

Timmy Nguyen Dis 1I
Posts: 107
Joined: Sat Aug 17, 2019 12:17 am

Re: Why is K unitless?

Postby Timmy Nguyen Dis 1I » Sun Jan 19, 2020 4:13 pm

K is simply a ratio between molarities, so that's why it has no units.

Sreyes_1C
Posts: 90
Joined: Fri Sep 28, 2018 12:19 am

Re: Why is K unitless?

Postby Sreyes_1C » Sun Jan 19, 2020 6:40 pm

because its concentrations over concentrations, the M cancels out and its also just a ratio of the concentrations


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