Description
Calculate the rate constant (with appropriate units) for a first order reaction which is 30.0% complete in 363 s.
What is the value of the half-life of the reaction?
How long will it take for the reaction to go to 95.5% completion?
Explanation & Answer
30 % of reaction completion, means Ao = 1M and A = 0.3
The formula for calculation of the first order reaction is:
A = Ao e-k t
Where, A is
the final amount (0.3)
Ao is the initial amount (1)
t = time ( 363 s)
k = rate constant that you are looking for
First, translate seconds of a given time into hours: 1 hour x 363 seconds / 3600 seconds = 0.1008 hours
Second,
A/Ao = e-k t
0.3/1 = e –k 0.1008
ln 0.3 = - k 0.1008
1.2 = - k 0.1008
k = 11.88 M/hr
t1/2 = ln2 / k = 0.693 / 11.88 = 0.058 hr M-1
Now, for 95.5% of reaction completion:
A/Ao = e-k t
0.955/1 = e -0.058 t
ln (0.955) = - t 0.058
-0.046 = - t 0.058
t= 0.79 hours or 2857.9 seconds
Happy New Year!
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