## Units

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Theodore_Herring_1A
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

### Units

How do you figure out the units for k in different ordered reactions?

Neil Hsu 2A
Posts: 61
Joined: Fri Sep 28, 2018 12:16 am

### Re: Units

Looking at the rate law, the units for the rate should end up being M/s, so depending on the order of the reaction, the units of k should be different. If you write out the units of each concentration and the rate, you should be able to figure out the units for k. For example, for a first order reaction, rate = k [A] and since rate is M/s and [A] is M, k should be 1/s. Doing this same thing will give you M^-1s^-1 for second order reactions, M^-2s^-1 for third order reactions, and M/s for zeroth order reactions.

Lorena Zhang 4E
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### Re: Units

Essentially, the final unit for all reaction is M/s or mol/(L*s). Therefore, you can start from the end and make it back to the unit of k based on the orders.

Cole Elsner 2J
Posts: 88
Joined: Fri Sep 28, 2018 12:25 am

### Re: Units

Your end goal is to have all units b in M/s. With this, you can figure out what the order of the reaction is and adjust k units to reach that end goal units.