Question

Afirst order reaction completed the 90%in 30minute find the time for99.9%,,,,

Answer 1

ln(No/N) = kt
You know No = 100
N = 100-90 = 10
K = ?
t = 30
Solve for k.

Use the same equation above, plug in k from above, the new N and solve for the new t.

Post your work if you get stuck.

Answer 2

https://socratic.org/questions/a-first-order-reaction-is-50-completed-after-30-minutes-this-implies-that-the-ti

ln(.1)=-k (30)
k== 0.0767528364

ln(.1/100)= -0.0767528364 t
t= ln(.001)/0.0767528364=90 min
Now think: it took 30 min to go to 90 percent. In another 30 min, it will go 9 percent (to 99). In another 30 min, it will go another .9 percent (99.9)