### Why is K unitless?

Posted:

**Thu Jan 09, 2020 4:02 pm**Why does the equilibrium constant, K, not have units?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=55804

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Posted: **Thu Jan 09, 2020 4:02 pm**

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

Posted: **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!

Posted: **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.

Posted: **Thu Jan 09, 2020 4:39 pm**

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

Posted: **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.

Posted: **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 :)

Posted: **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.

Posted: **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?

Posted: **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.

Posted: **Sun Jan 19, 2020 4:13 pm**

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

Posted: **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