### 15.105

Posted:

**Sun Mar 11, 2018 12:15 pm**Does anyone know how to solve exercise 15.105?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=155&t=29370

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Posted: **Sun Mar 11, 2018 12:15 pm**

Does anyone know how to solve exercise 15.105?

Posted: **Sun Mar 11, 2018 10:22 pm**

To solve 15.105, we are given:

initial mass of drug = 150 mg

half life = 4.5 hrs

1st order reaction

and t= 2 hrs

First, use the half life equation for a first order reaction to solve for the rate constant. Then, we can use the integrated rate law either a) solve for a ratio between the initial and final concentrations or b) pretend 150 mg is the initial concentration and find [A] (you'll get the same answer either way, and I think this method is easier). Since [A] is the amount that remains after two hours, 150 - [A] should give you the amount you need to re-inject the dog with.

Hope this helps!

initial mass of drug = 150 mg

half life = 4.5 hrs

1st order reaction

and t= 2 hrs

First, use the half life equation for a first order reaction to solve for the rate constant. Then, we can use the integrated rate law either a) solve for a ratio between the initial and final concentrations or b) pretend 150 mg is the initial concentration and find [A] (you'll get the same answer either way, and I think this method is easier). Since [A] is the amount that remains after two hours, 150 - [A] should give you the amount you need to re-inject the dog with.

Hope this helps!