[toeknee2120]

In class we learned a rate law is given to be:

rate=k[A]^x[ B]^y

and that you add the exponents to get the overall reaction order. We have only learned about zero, first, and second order reactions, so if you get something like these and get asked what the overal reaction order is, what is the answer?

rate=k[A]^1/2[ B]²

rate=k[A]¹[ B]¹[C]¹

I had a test yesterday and was asked what the units of k would be if the unit of time is seconds and unit of concentration is moles per liter. The rate law for a reaction is

rate=k[ClO₃^-][I^-][H⁺]²

I knew the unit of k for zero, first and second order, but if I add up these exponents, I get 4, right? I was so confused...

[Stovn0611]

Think about units. Rate is measured in molarity/second generally and concentrations are all measured in molarity so just think about what units k would have to be to have the units on the left side and right side of the equation be the same.

[Big-Daddy]

The overall reaction order is certainly found by summing the reaction orders with respect to every individual species in the rate law. No doubt about that. k is then found by a rearrangement. If you have the overall reaction order, n_order(overall), the units of k will be (mol·dm^-3)^{1-n_order(overall)}·s^-1. Try deriving this from the rate equation to check. Similarly, if working with pressures, k would be in Pa^{1-n_order(overall)}·s^-1.

Any other questions?