How to know when to use which formula?

[Adriana Rangel 1A]

How do you know if you have to solve for k or any variable really to use "[A]= -kt + [A0]" vs "ln[A]=-kt+ln[A0]" ??

[Joanne Guan 1B]

I'm not really sure what you're trying to ask, but here are some hopefully helpful points.

Zero-order integrated rate law: [A] = - kt + [A]₀
First-order integrated rate law: ln[A] = -kt + ln[A]₀
Second-order integrated rate law: 1/[A] = kt + 1/[A]₀

These can be found on the constants and equations sheet. To know which one to use, you have to know the order of the reaction.

[Sarah Maraach 2K]

Your formula depends on the order of the reaction. So, if you’re given k and asked to solve for [A] at either initial or final or for t, then you’d look at the units of k to determine what order the reaction is. If you’re solving for k, you will most likely be given the order of the reaction as there is no other way to tell unless you’re given a graph.