Units of K


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shannon_tseng_3L
Posts: 20
Joined: Wed Sep 21, 2016 2:56 pm

Units of K

Postby shannon_tseng_3L » Mon Feb 20, 2017 10:54 pm

Is there an easy way to find the units of different K values for different reaction orders?

Rachel Wile 2D
Posts: 49
Joined: Sat Jul 09, 2016 3:00 am

Re: Units of K

Postby Rachel Wile 2D » Mon Feb 20, 2017 11:18 pm

For a zero order, the units of k are M/s, or mol*L^-1*s^-1. For first order, the units are 1/s or s^-1. For second order, the units are 1/M*s or L*mol^-1*s^-1. You will notice that there is a pattern here. Every time the order is increase by one we divide by M or mols/L. So therefore, for a third order, the units of k would be 1/M^2*s or L^2*mol^-2*s^-1. Hope this helps!

Amy Ko 3C
Posts: 24
Joined: Sat Jul 09, 2016 3:00 am

Re: Units of K

Postby Amy Ko 3C » Tue Feb 21, 2017 8:13 am

Memorizing the k units helps. You can also set up the rate equations to find the k units
For example: a 2nd order rate equation is rate = k [R]^2
The unit of rate is mol/Ls and each [R] has the unit of mol/L
Then, mol/Ls = k (mol/L)(mol/L)
k must cancel out 1 L in denominator and 1 mole in numerator and must add s in denominator
Thus, the unit of k must be L/(mol x s)

Ryan Cerny 3I
Posts: 25
Joined: Wed Sep 21, 2016 3:00 pm
Been upvoted: 1 time

Re: Units of K

Postby Ryan Cerny 3I » Tue Feb 21, 2017 9:36 am

K(units) = (L/mol)^(overall n -1) x s^-1

Joslyn_Santana_2B
Posts: 51
Joined: Wed Sep 21, 2016 2:58 pm

Re: Units of K

Postby Joslyn_Santana_2B » Tue Feb 21, 2017 10:03 am

Starting from M/s you just then divide my M continuously to get the next order units.


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