In a 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

Step-by-step solution

Order 1 Concentration changes from 0.8 M to 0.4 M in ( 50 % ) 15 minutes this half life is = 15 minutes = t 50 A change from 0.1 M to 0.025 M is 75% and for first order reaction t 75 = 2 × t 50 = 2 × 15 = 30 m i n u t e s t 50 = 15 m i n u t e s k = 2.303 l o g 2 t 50 = 2.303 l o g 2 15 α = 0.1 M α - x = 0.025 M for first order: k = 2.303 l o g t α α - x 2.303 l o g 2 15 = 2.303 t l o g 0.1 0.025 = 2.303 t l o g 4 2.303 l o g 2 15 = 2 × 2.303 l o g 2 t t = 30 minutes.