Question
In first order reaction, the concentration of the reactant decreases from 0.8 M to 0.4 M in 15 minutes. The time taken for the concentration to change from 0.1 M to 0.025 M is
-
30 minutes
-
60 minutes
-
7.5 minutes
-
15 minutes
Solution
A.
30 minutes
Order = 1
Concentration changes from 0.8 M to 0.4 M(50%) in 15 min, thus half - life is 15 min = T50
A change from 0.1 M to 0.025 M is 75% and for first order reaction
T75 = 2 x T50
= 2 x 15 = 30 min
T50 = 15 min
