k


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Tiffany Cao 1D
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k

Postby Tiffany Cao 1D » Sat Mar 03, 2018 10:45 pm

When finding the rate constant, should we convert all time units to seconds?

Jessica Yang 1J
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Re: k

Postby Jessica Yang 1J » Sat Mar 03, 2018 10:48 pm

I think it depends on the units in the rest of the problem. If it is stated that the rate is mol/L- min, then the k will probably by 1/min. However, if nothing is given in terms on units in the rest of the problem, I think it would be best to use time units as seconds.

Kayla Tchorz-Dis 1F
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Re: k

Postby Kayla Tchorz-Dis 1F » Sat Mar 03, 2018 11:51 pm

The units of k are completely dependent on what order you are dealing with. Zero order is M/s, first order is in s^-1, and second order is L/mol●s

CameronJohari1J
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Re: k

Postby CameronJohari1J » Sun Mar 04, 2018 1:05 pm

In general, it is useful to keep k units for time in terms of seconds. You can always convert to other units of time if the problem specifically asks for it, aka minutes or hours.

Fatima_Iqbal_2E
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Re: k

Postby Fatima_Iqbal_2E » Sun Mar 04, 2018 2:02 pm

I think it would be a good idea to convert time to seconds if the problem doesn't ask otherwise. If needed, after finding k (with seconds as your units of time), you can always use conversion factors to change the seconds into another unit of time.

Arshpreet Sandhu 1B
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Re: k

Postby Arshpreet Sandhu 1B » Sun Mar 04, 2018 9:29 pm

I would keep it in seconds unless another unit is specified in the problem

AnuPanneerselvam1H
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Re: k

Postby AnuPanneerselvam1H » Sun Mar 04, 2018 9:41 pm

Most problems keep k in terms of seconds however it is ok to convert to other units if needed for the problem.

Wenjie Dong 2E
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Re: k

Postby Wenjie Dong 2E » Sun Mar 04, 2018 11:14 pm

There is no need to do so unless other calculation is needed.

Merzia Subhan 1L
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Re: k

Postby Merzia Subhan 1L » Mon Mar 05, 2018 12:18 am

I'm sure that if they use a different unit in the problem like hours or minutes, you could leave the k in that unit instead of in seconds

Alyssa Pelak 1J
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Re: k

Postby Alyssa Pelak 1J » Mon Mar 05, 2018 9:05 am

If they want a specific unit they will likely state it in the problem. If not, you can use the easiest unit.

Adam Enomoto 1L
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Re: k

Postby Adam Enomoto 1L » Mon Mar 05, 2018 12:50 pm

Reaction A: k = 2.3 M-1s-1
Reaction B: k = 1.8 Ms-1
Reaction C: k = 0.75 s-1

How do we know which one is a zero order reaction just given the units?

Gurkriti Ahluwalia 1K
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Re: k

Postby Gurkriti Ahluwalia 1K » Mon Mar 05, 2018 11:39 pm

a zero order reaction should have the same units as the rate, mol/L/s or mol x L-1 x s-1

Alex Nechaev 1I
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Re: k

Postby Alex Nechaev 1I » Tue Mar 06, 2018 10:32 pm

Adam Enomoto 1L wrote:Reaction A: k = 2.3 M-1s-1
Reaction B: k = 1.8 Ms-1
Reaction C: k = 0.75 s-1

How do we know which one is a zero order reaction just given the units?

I would just try to memorize the units for at least the first few orders.

Sophia Bozone 2G
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Re: k

Postby Sophia Bozone 2G » Tue Mar 06, 2018 10:44 pm

I don't think the math of the problem is messed up, simply on a logistics level, when a different unit is used. its all about keeping track of your units. Also it will be easier to keep the units the same as the units of the answer you are trying to find

Phillip Winters 2F
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Re: k

Postby Phillip Winters 2F » Wed Mar 07, 2018 12:09 am

It isn't always necessary to change the units of k to s^-1, but just make sure that units always cancel

Rishi Khettry 1L
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Re: k

Postby Rishi Khettry 1L » Sat Mar 17, 2018 1:05 am

Usually the problem will specify a unit of time and we would want to use that same unit of time for K. Otherwise, using units of time as seconds is usually a safe bet.

GabrielGarciaDiscussion1i
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Re: k

Postby GabrielGarciaDiscussion1i » Sat Mar 17, 2018 1:56 am

It's dangerous to make blanket statements of ALL PROBLEMS TO SECONDS, but usually the problem will specify with seconds, minutes, or heck, maybe even hours with LARGE half lives. So just read the question and dimensional analysis when necessary.


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