Units of Rate Laws

[306092134 14B 3E]

I am having trouble finding the rate laws in the book. Can someone please break down the unit for the rate constant for first, zero, and second order?

[RandyRich]

The 0 order is M/S, the first order is 1/S, and the 2nd is 1/MS. This is because standard units of rate are M/S, so to derive these units at the 0 order you just do k[A]^0 = k x 1 = (M/S). So for 1st order its k[A]^1 = (M/S) = k(M). Finally 2nd order is k[A]^2 = (M/S) = k(M^2).

[106169087]

For zero order reactions, the units are M/s. For first order reactions, the units are 1/s. For second order reactions, the units are 1/Ms.

[Katie L 2I]

I think that learning how to derive the actual equations helped too with the memorization. Rate is always M/s, and [A, B,C etc.] will always be M. So with the rate law equation set up as k = rate/concentration, the units cancel out.

For example, for a first order reaction, we have rate = k[A]. Writing out all the units, we have M/s = k * M. Moving the M to the otherside, they cancel, leaving us with the units of 1/s, which is correct. Hope this helps!

[305920501]

One trick for figuring out rate laws is L^(N-1) x mol^(1-N) x s^-1 where N is the order of the reaction you are referring to. This makes the zeroth order mol x L^-1 x s^-1, the first order s^-1, and the second order is L x mol ^ -1 x s^-1.