How to Calculate Concentration in a First Order Reaction?

[Attraction]

Homework Statement

The decomposition of AB is first order with a k = 2.3 x 10-7 s-1 at 45oC. If the initial concentration is 0.25 M, the concentration after 2.3 min is:

Homework Equations

ln[A]_t = -kt x ln[A]₀

The Attempt at a Solution

I have subbed in the values I have but I am not getting the right answer. I am unable to solve the logarithmic equation and need help there but also need to know if my method is correct.

I have subbed in:

ln[A]_t = -2.3 x 10^-7 x 138 (seconds) x ln.25

I am getting :

ln[A]_t = 4.4 x 10^-5

My problem is that I cannot remember how to solve that equation for [A]_t. It's been a while since i looked at logarithmic equations. I have done google searches for the past hour and tried a few things but can't solve it. I'm not sure if my method is even correct in the first place.

Please help.

 

[Borek]

What is logarithm definition?

 

[Attraction]

YES! I have figured it out. Sometimes I wonder if I have the aptitue to learn this chemistry stuff, but I am doing well so far and I am teaching myself so it's obviously not going to be easy all the way. Anyway.. this was where I left off last time.


ln[AB]_t = -2.3 x 10^-7 x 138 (seconds) + ln.25
= -1.386

ln[AB]₁₃₈ = -1.386
[AB] = e^-1.386 **This is the step that was killing me, simple logarithmic algebra)**

[AB] = .25M


Now, let's see how I get on with the rest of the problems!