Use ln(No/N)=kt to determine the value of k. For example, start with 100 atoms/molecules/whatever in the reaction that is decomposing) so No = 100 and N = 100-42.6 = 57.4. t, or course, is 18.5 min.
Then, knowing the value of k, use the same formula to calculate t. (No will be 100 and N will be 25). Post your work if you get stuck.
Can someone please show me a detailed solution to this problem? Thanks.
In a first order decompostion reaction, 42.6% of a compound decomposes in 18.5 minutes. How long, in minutes, will it take for only 25.0% of the compound to remain?
The answer is: 46.2 (I just don't know how to get it).
2 answers
A = Ao e^kt where A is amount REMAINING
(1-.426) Ao = Ao e^18.5k
ln .574 = 18.5 k
-.555=18.5 k
k = -.03
then
.25 = e^-.03t
ln .25 = -.03 t
-1.386 = -.03 t
t = 46.2 minutes sure enough
(1-.426) Ao = Ao e^18.5k
ln .574 = 18.5 k
-.555=18.5 k
k = -.03
then
.25 = e^-.03t
ln .25 = -.03 t
-1.386 = -.03 t
t = 46.2 minutes sure enough