10% of a sample reacts in 25 s. If the reaction follows first order kinetics, how long would it take for half the sample to react?

Answer 1

ln(No/N) = kt
If we start with an arbitrary number, say 100, and 10% is used, that would leave 90
ln(100/90) = k(25sec)
solve for k. You want the half life; therefore, substitute the k you find in the same equation but this time start with 100 and N = 50 (half is gone). Solve for t and that will be t_1/2