A reaction in solution, A + B→P, is studied and found to have the rate law Rate = k [A] with a rate constant of 3.5×10^{- 3} s^{- 1}. If an experiment begins with a concentration of A equal to 0.20 M , at what time after the start of the experiment will the concentration of A be 0.050 M ?

Question

Quizplus · Accepted Answer

We can use the integrated rate law equation for first-order reactions:

[A]t = [A]0 e^(-kt)

We can rearrange this to solve for time:

t = (-1/k)ln([A]t/[A]0)

We are given the initial concentration of A (0.20 M) and the final concentration of A (0.050 M), so we can plug these values into the equation and solve for time:

t = (-1/3.5x10^-3 s^-1)ln(0.050 M/0.20 M) = 3.9x10^2 s = 3.9x10^1 s (to 2 significant figures)

Therefore, the answer is C) 3.9x10^1 s.

A Reaction in Solution, a + B→P, Is Studied and Found