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Units of k

Posted: Mon Mar 05, 2018 12:35 am
by Nancy Le - 1F
How do you calculate the units of k for the order of each reactant?

Re: Units of k

Posted: Mon Mar 05, 2018 12:54 am
by Elizabeth Ignacio 1C
You find the units of k by cancelling out all other known units in the rate law, like all of the different mol/L and the units for time. You can also just memorize them, because they're the same for each rxn order.

Zero order: mol/L/s or basically, Molarity/Time
First Order: 1/s, or basically 1/Time
Second Order: L/mol/s, which is (molarity flipped)/Time

Re: Units of k

Posted: Mon Mar 05, 2018 1:56 am
by Ya Gao
You can calculate the unit of k based on the rule that the rate of reaction has an unchanging unit which is mol*L-1*s-1

Re: Units of k

Posted: Mon Mar 05, 2018 9:10 am
by Alyssa Pelak 1J
The simplest way is to write out the rate law and divide.

1st order: rate=k[A] and divide rate by [A]. rate is written in mol.L-1.s-1. and [A] is mol.L-1. If you divide the two you are left with s-1.

2nd order: rate=k[A]^2. as with first order divide rate (mol.L-1.s-1.) by [A]^2 to get L.mol-1.s-1.

0 order: rate=k. that leaves you with mol. L-1.s-1

Re: Units of k

Posted: Mon Mar 05, 2018 10:00 am
by Cali Rauk1D
Each unit of K will be different for each order

Re: Units of k

Posted: Mon Mar 05, 2018 2:33 pm
by Yutian Zhao -1J
you can write the rate law (with units) first and then cancel units on both sides, then whatever units that are not cancelled should be the units of k. the units of k depends on the order of reaction. And pay more attention when writing the rate law if any concentration is to be squared (or higher), since your units for that concentration should also be squared. Hope it helps.

Re: Units of k

Posted: Mon Mar 05, 2018 4:58 pm
by Akash_Kapoor_1L
What is the best way to convert between different units of k? Would we ever have to convert k from L/ mol*s, into 1/ kPa*s?

Re: Units of k

Posted: Mon Mar 05, 2018 5:00 pm
by Michelle Steinberg2J
Last year in chemistry I learned that the units of k = 1/M^(overall order-1)*unit of time.
:)

Re: Units of k

Posted: Wed Mar 07, 2018 2:42 pm
by Sarah 2F
It is different for each reaction order