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### 15.9

Posted: Wed Feb 28, 2018 10:04 pm
I'm trying to do problem 15.9, but can't follow the logic of the solutions manual. Can someone break it down for me? The question reads:
Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for (a) zero-order reactions; (b) first-order reactions; (c) second-orde reactions.
If someone could just explain how to do part (a), I can probably deduce how to do parts (b) and (c).

### Re: 15.9

Posted: Wed Feb 28, 2018 10:17 pm
So to calculate the reaction rate, we usually do reaction rate = ∆concentration of reactants or products/∆time. This would give you Molarity/Time, which is usually mol*L-1seconds-1. If you look at the the general equation for the differential rate law, it is rate = k[R]n. Part a of this question asks for the zero order reaction, which would be rate = k0[A]0. Since [A]0 = 1, we have rate = k0. Units of k would equal to units of rate, mol*L-1seconds-1. Hope that helps

### Re: 15.9

Posted: Thu Mar 01, 2018 1:57 am
Rate is always expressed in mol/(L*s), so k changes units depending on the order of the reaction.

### Re: 15.9

Posted: Thu Mar 01, 2018 10:26 am
The units of k depend on the overall order of reaction. Page 620 of the textbook shows which units of k correspond to first, second, and third order reactions respectively. Generally, units of k will match up with the units concentration so that the units of rate will be concentration / time (mol / L*s).