units of K

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Natalie LeRaybaud 1G
Posts: 54
Joined: Thu Jul 13, 2017 3:00 am

units of K

Postby Natalie LeRaybaud 1G » Wed Feb 28, 2018 2:12 pm

Are the units of K constantly changing or are they always the same? And if they are changing, what are they according to each specific order?

Sean Monji 2B
Posts: 66
Joined: Fri Sep 29, 2017 7:06 am

Re: units of K

Postby Sean Monji 2B » Wed Feb 28, 2018 2:34 pm

The units do change based on the order:
EDIT: this post did it better I think
https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=5287

Britney Alvey 1B
Posts: 31
Joined: Fri Jun 23, 2017 11:39 am

Re: units of K

Postby Britney Alvey 1B » Wed Feb 28, 2018 5:54 pm

For 0 order reactions, the units for k are are mol/(L*s). For 1st order reactions, the units of k are s^(-1). For 2nd order reactions, the units for k are L/(mol*s).

Nicole Anisgard Parra 2H
Posts: 39
Joined: Sat Jul 22, 2017 3:01 am

Re: units of K

Postby Nicole Anisgard Parra 2H » Wed Feb 28, 2018 7:58 pm

The units of K change based on what gets cancelled out in the rate law equations; this is why the value of K is different based on the order of the reaction.

Renee Delamater 2H
Posts: 31
Joined: Wed Nov 16, 2016 3:02 am

Re: units of K

Postby Renee Delamater 2H » Wed Feb 28, 2018 9:15 pm

Britney Alvey 1B wrote:For 0 order reactions, the units for k are are mol/(L*s). For 1st order reactions, the units of k are s^(-1). For 2nd order reactions, the units for k are L/(mol*s).
why are these the units? does it have to do with each graph for first order, zero order, and second order reactions?

Amanda Wu 2C
Posts: 31
Joined: Sat Jul 22, 2017 3:00 am

Re: units of K

Postby Amanda Wu 2C » Wed Feb 28, 2018 9:17 pm

The units of K, the rate constant, change depending on the order of the overall reaction. This is because the unique reaction rate always has units of M/s or mol(L^-1)(s^-1). Thus, the units of K have to be adjusted to account for its multiplication with zero, one, or more reactant concentrations in the differential rate law so that the unique reaction rate ends up with the correct units.

The units of K for the different orders of reactions:
zero-order: M/s
1st-order: 1/s
2nd-order: 1/(Ms)
3rd-order: 1/((M^2)(s))

where M is mol/L


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