Units of K

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Paul Adkisson 1D
Posts: 23
Joined: Wed Sep 21, 2016 3:00 pm

Units of K

Postby Paul Adkisson 1D » Wed Feb 22, 2017 12:15 am

I was somewhat confused on the sign of k.
Since the General Rate equation for RXN aA --> bB is
Rate = -1/a d[A]/dt = 1/b d[B]/dt, and we know d[A]/dt = k[A]^(molecularity)
would the sign of k change whether we are considering the product or reactant? Or is it always positive? Is there something I'm missing here?

Natalie Rotstein 3J
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

Re: Units of K

Postby Natalie Rotstein 3J » Wed Feb 22, 2017 12:23 am

It's positive for the thing being considered; for the equation you mentioned, the reason one side is negative is because the concentration of the reactants decreases while the concentration of the products increases, making the change in reactants negative and products positive. To counter this so that k is the same value/sign on either side, the - is added to the equation.

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