Question

It takes 42.0 min for the concentration of a reactant in a first-order reaction to drop from 0.45 M to 0.32 M at 25C. How long will it take for the reaction to be 90% complete?

Answer 1

For a first order reaction
ln (No/N) = kt
ln (0.45/0.32) = k(42min)
Solve for k, then
ln (No/N) = kt
ln (100/90) = k from above*t
Solve for t. Post your work if you get stuck.

Answer 2

I can’t figure it out still