Posted by csb on .
A reaction is first order and it takes 324 minutes for the reaction to be 50.0% complete. How long will it take for the reaction to be 85.0% complete at the same temperature? The answer is 887 minutes but I have no idea how he got that? help

chemistry 
DrBob222,
ln(No/N) = kt
For convenience, start with 100 for No.
ln(100/50) = k(324)
solve for k, the rate constant.
Second part.
ln(100/15) = k(from above)t
Solve for t.
I get 886.8 which rounds to 887 minutes.