The rate constant for this first-order reaction is 0.650 s–1 at 400 °C.

A------> Products

How long (in seconds) would it take for the concentration of A to decrease from 0.660 M to 0.350 M?

ln(No/N) = kt

No = 0.660
N = 0.350
t = unknown.
k = given
solve for t.

To determine the time it would take for the concentration of A to decrease from 0.660 M to 0.350 M, we can use the integrated rate law for a first-order reaction:

ln([A]t/[A]0) = -kt

Where [A]t is the concentration of A at a given time (t), [A]0 is the initial concentration of A, k is the rate constant, and t is the time.

Rearranging the equation:

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

Now, let's plug in the values:

[A]0 = 0.660 M
[A]t = 0.350 M
k = 0.650 s–1

t = -(ln(0.350 M/0.660 M))/0.650 s–1

Now we can solve for t using these values.