## k

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Tiffany Cao 1D
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### k

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

Jessica Yang 1J
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### Re: k

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

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

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

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

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

AnuPanneerselvam1H
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### Re: k

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

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

Merzia Subhan 1L
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### Re: k

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

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

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### Re: k

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

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

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

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

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

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.

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### Re: k

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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