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### Homework question

Posted: **Mon Mar 11, 2019 7:36 pm**

by **sarahtang4B**

On 7B3b, its a first order reaction so how is it ln(A0/At) = kt and not -kt? I thought it was -kt for first order reactions?

If not, how did we get that equation?

### Re: Homework question

Posted: **Mon Mar 11, 2019 7:43 pm**

by **Henry Krasner 1C**

This is a different way to display the first order reaction equation.

You start with

ln[A]=ln[A(initial)] - kt

Then you move ln[A(initial)] to the other side and use log rules to get

ln([A]/[A(initial)])=-kt.

Then divide by -k or -t depending on what you want to find.

The textbook just organizes it differently, but either method will allow you to obtain the same result.

### Re: Homework question

Posted: **Tue Mar 12, 2019 11:31 pm**

by **Lia Inadomi 1I**

This is because it is ln([A]0/[A]t) instead of ln([A]t/[A]0) which is when it would be -kt. This is just because of log rules so ln([A]t/[A]0)=-ln([A]0/[A]t) because coefficient of a log can be seen as the exponent inside the log function