1. If a drug decomposes according to first-order kinetics, what is its concentra
ID: 993621 • Letter: 1
Question
1. If a drug decomposes according to first-order kinetics, what is its concentration after one hour, if the half-life is 21 minutes? Express as a % of original concentration?
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2. Which of the following statements accurately describes the reaction mechanism?
A. The reaction mechanism is associative, and the rate-determining step involves one mole of Y. B. The reaction mechanism is associative, and the rate-determining step involves two moles of Y.
C. The reaction mechanism is dissociative, and the rate-determining step involves one mole of Y.
D. The reaction mechanism is dissociative, & the rate-determining step involves two moles of Y.
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3. The concentration of some floral scent is 100 ppm. If the half-life for its decomposition is 4 minutes, how much time elapses before there is only 1 ppm in the air?
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4. When the reaction quotient is greater than the equilibrium constant, which of the following is NOT true?
a) The system has too many products and too few reactants
b) The reaction is displaced from equilibrium
c) The reaction must shift in the forward direction to reach equilibrium
d) The reverse reaction rate is greater than the forward reaction rate
Explanation / Answer
1) For a first order reaction,
t1/2 = 0.693/k
=> K = 0.693/ t1/2 (given t1/2 = 21 min )
= 0.693/21 min
= 0.033 min-1
using the first order rate equation,
K= 2.303/t log a/(a-x)
Let the conc. be taken as 100, t = 1 hr = 60 min
Now putting these values in above equation, we get ;
0.033 min-1 =2.303/60 min log 100/(a-x)
=> log 100 /(a-x) = 0.033×60/2.303
=> log 100/(a-x) =0.8597
Taking anti logs;
100/(a-x) = anti log (0.8597)
=>100/(a-x) =7.240
=> a-x = 100/7.240
= 13.81 % (Ans)
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