## Units in 15.17 vs. 15.19

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

Sarkis Sislyan 1D
Posts: 31
Joined: Thu Jul 27, 2017 3:00 am

### Units in 15.17 vs. 15.19

How do we know when we should switch our units from mmol to mol? For example, in question 15.17, the solutions manual keeps the concentrations of A and B as well as the rate in terms of mmol, but in question 15.19, the concentrations of A, B, and C as well as the rate are converted into mol. Is there a reason for this? If not, how do we know which unit to use?

Daniisaacson2F
Posts: 30
Joined: Sat Jul 22, 2017 3:00 am

### Re: Units in 15.17 vs. 15.19

I would just keep the units of the answer the same units that they give you, I know that sometimes they change the units interchangeably from minutes and seconds and as long as the answers are consistent with each other I believe its ok.

Dylan Davisson 2B
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am
Been upvoted: 2 times

### Re: Units in 15.17 vs. 15.19

The proper units for molar concentrations are mol*L^-1. It would be safe to always convert the given concentrations into these units and then work out the equation like the question asks.

The only difference I see is that the initial rate for 15.17 is given with respect to the product G, while the initial rate for 15.19 is given with respect to the reactant A. Perhaps because you know that both reactants and products in 15.17 are in mmols, it is acceptable to keep the units in mmols. However, you don't know the units for the products in 15.19, so you have to convert it into the standard molar concentration mol*L^-1. This is speculation, but it is the only difference I can see in the two problems.