At a given temperature, a first-order reaction has a rate constant of 2.8 times

Question

At a given temperature, a first-order reaction has a rate constant of 2.8 times 10^-3 s^-1. How long will it take for the reaction to be 29% complete? a) 440 s b) 53 s c) 1500 s d) 120 s e) 1200 s The OH middot radical disproportionates according to the elementary chemical reaction OH middot + OH middot rightarrow H_2O + O. This reaction is second-order in OH middot. The rate constant for the reaction is 2.0 times 10^-12 cm^3/molecules at room temperature. If the initial OH middot concentration is 1.9 times 10^13 molecules/cm^3, what is the first half-life for the reaction? a) 3.5 times 10^11 s b) 3.8 times 10^1 s c) 2.6 times 1^-2 s d) 5.3 times 10^-14 s e) 1.3 times 1^-2 s

Explanation / Answer

Q9

1st order

k = 2.8*10^-3

time required for 29% compeltion

so

ln(A) = ln(A0) - kt

substitute values

29% compelte means 0.29 of A is left

A = 0.29*A0

ln(0.29*A0) = ln(A0) - (2.8*10^-3)t

t = ln(0.29*A0/A0) / (2.8*10^-3)

t = 442.09 seconds

choose A

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