## Units for Rate Constants

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

Katie Frei 1L
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

### Units for Rate Constants

Is there an easy way to determine the units for rate constants for zeroth, first, and second-order reactions? Thank you!

abbydouglas1K
Posts: 65
Joined: Fri Sep 28, 2018 12:26 am

### Re: Units for Rate Constants

Basically the rate the reaction ((-1/a)(d[A]/dt)) is equal to mol x L^-1 x s ^-1. This rate is equal to the either k[A]^0, k[A]^1, k[A]^2 depending on whether or not the reaction is zeroth order, first order, or second order respectively. [A] represents the concentration of an unknown reactant and thus its units are mol x L^-1. The order of the reaction will be determined then by the power to which [A] is raised, which what you will divide the rate by as to solve for.
Ex: k= ((-1/a)(d[A]/dt)) / ([A]) = ( mol x L^-1 x s ^-1) / ( mol x L^-1) = s^-1

Tatum Keichline 2B
Posts: 64
Joined: Fri Sep 28, 2018 12:26 am

### Re: Units for Rate Constants

mol/Ls zero and first
1/mol/Ls second order

Henry Dudley 1G
Posts: 61
Joined: Fri Sep 28, 2018 12:16 am

### Re: Units for Rate Constants

In the textbook there are questions with answers that have units in L per mol. Why is this and how do you generally determine the units for rate constants?

BenJohnson1H
Posts: 68
Joined: Fri Sep 28, 2018 12:17 am

### Re: Units for Rate Constants

In the review session today, the TA said that using L is also acceptable. It's simply expanding molarity:)

Elizabeth Kim 4E
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

### Re: Units for Rate Constants

mol/L and then 1/mol/L for second order