### 15.23 b

Posted:

**Wed Mar 07, 2018 9:27 pm**Why is the formula used for this question ln[A]0 / [A]t , instead of ln [A]t/[A]0?

Created by Dr. Laurence Lavelle

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

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=145&t=29194

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Posted: **Wed Mar 07, 2018 9:27 pm**

Why is the formula used for this question ln[A]0 / [A]t , instead of ln [A]t/[A]0?

Posted: **Wed Mar 07, 2018 9:42 pm**

I used the equation and got the same answer as the solutions manual. I think the two equations are equivalent because of the negative sign I used in my answer, when transferred to the other side, would flip the two concentrations.

Posted: **Fri Mar 09, 2018 4:50 pm**

It's just algebraic manipulation; flipping the numerator and denominator will give you the negative log value.

Posted: **Fri Mar 09, 2018 10:22 pm**

If you make both sides of the equation ln([A]t/[A]0) = -kt negative, you will have: ln([A]0/[A]t) = kt. Making the natural log negative flips the content because:

ln([A]t/[A]0) = ln[A]t - ln[A]0

ln([A]t/[A]0) = ln[A]t - ln[A]0