Final answer:
After a first-order reaction is 35% complete, 65% of the initial concentration of the reactant remains. Starting with 0.604 M, the remaining concentration of A is 0.393 M, making option c (0.393 M) the correct answer.
Step-by-step explanation:
To determine the concentration of A after a first order reaction is 35% complete in 20 minutes, we begin by understanding what a first order reaction entails. In a first-order reaction, the rate of reaction is directly proportional to the concentration of the reactant. Therefore, the rate constant can be used alongside the time of the reaction to find the remaining concentration using the formula for first-order kinetics:
ln([A]0/[A]) = kt, where:
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- [A]0 is the initial concentration
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- [A] is the concentration at time t
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- k is the rate constant
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- t is the time
Since the reaction is 35% complete, 65% of the original concentration remains. Starting with an initial concentration of 0.604 M, we calculate the remaining concentration:
0.65 x 0.604 M = 0.393 M
Therefore, option c. 0.393 M is the correct answer to the question of what the concentration of A will be after 20 minutes when starting with an initial concentration of 0.604 M and the reaction is 35% complete.