The half-life of a reaction, t 1/2, is the time it takes for the reactant concen
ID: 1025873 • Letter: T
Question
The half-life of a reaction, t1/2, is the time it takes for the reactant concentration [A] to decrease by half. For example, after one half-life the concentration falls from the initial concentration [A]0 to [A]0/2, after a second half-life to [A]0/4, after a third half-life to [A]0/8, and so on.
A certain first-order reaction (Aproducts) has a rate constant of 7.50×103 s1 at 45 C. It will take 6.16 minutes for the concentration of the reactant, [A], to drop to 6.25% of the original concentration.
A certain second-order reaction (Bproducts) has a rate constant of 1.25×103M1s1 at 27 C and an initial half-life of 216 s . What is the concentration of the reactant B after one half-life?
Explanation / Answer
1)
rate constant = 1.25×103M1s1
initial half - life = 216 sec
half - life = 1 / k Ao
Ao = 1 / k t1/2
= 1 / 1.25×103 x 216
= 3.70 M
concentration of reactant B = 3.703 M
after one - half - life :
concentration of the reactant B = 1.85 M
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