Question

A substance 'A decomposes in solution following the first order kinetics. Flask I contains 1 L of 1 M solution of A and flask II contains 100 mL of 0.6 M solution. After 8 hr the concentration of A in flask I becomes 0.25 M. What will be the time for concentration of A in flask II to become 0.3 M?

• A. 0.4 hr
• B. 2.4 hr
• C. 4.0 hr
• D. Unpredictable as rate constant is not given

Answer 1

The correct option is C 4.0 hr

Flask I:
$\therefore t_{1/2}=4hr$
Flask II:
$0.6M\underset{t_{1/2}=4hr}{\to }0.3M$
A first order reaction is independent of the initial concentration of the reactant.
Hence, answer is (C).