### How to solve for time, given k and concentrations

Posted: **Sat Feb 13, 2016 1:33 pm**

by **Katie Clark 3B**

How do you solve for time given k and the concentrations. For example, in the Winter 2014 Quiz 2 Prep #9, the question is: A reaction has k=8.39 M^{-1}s^{-1}. How long does it take for the reactant concentration to drop from 0.0840 M to 0.0220 M?

### Re: How to solve for time, given k and concentrations

Posted: **Sat Feb 13, 2016 2:31 pm**

by **Jake Ney lecture 1 discussion 1F**

Because the he K value is given in M-1s-1 we know that we are dealing with a 2nd order reaction. Solving the question now is just a matter of plugging in the given values into the equation 1/[A]=kt+1/[Ao] => 1/[.0220 M]=(8.39M-1s-1)t+1/[.0840 M] and solving algebraically for t.