The decomposition reaction of NOBr is second order in NOBr, with a rate constant at 20°C of 25 M-1 min-1. If the initial concentration of NOBr is 0.025 M, find
(a) the time at which the concentration will be 0.010 M.
(b) the concentration after 145 min of reaction.
a)
we have:
[NOBr]o = 0.025 M
[NOBr] = 0.01 M
k = 25 M-1.min-1
use integrated rate law for 2nd order reaction
1/[NOBr] = 1/[NOBr]o + k*t
1/(0.01) = 1/(0.025) + 25*t
100 = 40 +25*t
25*t = 60
t = 2.40 min
Answer: 2.40 min
b)
we have:
[NOBr]o = 0.025 M
t = 145.0 min
k = 25 M-1.min-1
Given:
[NOBr]o = 0.025 M
use integrated rate law for 2nd order reaction
1/[NOBr] = 1/[NOBr]o + k*t
1/[NOBr] = 1/(0.025) + 25*145
1/[NOBr] = 40 + 25*145
1/[NOBr] = 3665
[NOBr] = 2.73*10^-4 M
Answer: 2.73*10^-4 M
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