posted by Josh .
The rate constant for this first order reaction is 0.0470 s-1 at 400 C.
A TO Products
After how many seconds will 11.0% of the reactant remain?
This is the long way around but this is what I would do.
ln(No/N) = kt
I would call No = 100
Then N would be 11.
Substitute k and solve for t in seconds.