Question

given the rate equation rate=k[a]^-2[b] what are the units for k.

Answer 1

rate is typically expressed in terms of mol/L*min, or \[R = \frac{mol}{L*\min}\] or some other unit of time. That rate has to also be equal to the rate law, which you've been given as
\[R = k \frac{[B]}{[A]^{2}}\]
the units of K have to be such that when you multiply by the concentrations, you're left with only mol/L*min

Answer 2

I find it unlikely that you would have a negative second order though.

Answer 3

@shamalamadingdong true, but if it were, that would get you the proper units for k.

Answer 4

I agree that's why I gave you a medal.