If the rate constant of a reaction is 0.03 s-1, how much time does it take for 7.2 mol L-1 concentration of the reactant to get reduced to 0.9 mol L-1 ? (Given: 2 = 0.301)
- 210 s
- 21.0 s
- 69.3 s
- 23.1 s
Answer
(3) 69.3 s
Solution
The unit s-1 shows a first order reaction.
t = 2.303k [R]0[R] = 2.3030.03 7.20.9 = 2.3030.03 8
8 = 3 2 = 3 0.301 = 0.903
t = 2.303 0.9030.03 = 69.3 s
(Check: 7.2 0.9 is three half-lives; t1/2 = 0.6930.03 = 23.1 s, 3 23.1 = 69.3 s)
Answer: (3)