2. In a study of the alcohol dehydrogenase catalysed oxidation of of ethanol at

Question

2. In a study of the alcohol dehydrogenase catalysed oxidation of of ethanol at 25.0c the molar concentration of cthanol decreased in a first-order reaction from 220.0 mmol/L to 56.0 mmol/L in 1.22 x 10s, what is the rate constant of the reaction at 25C? 3. The thermal decomposition of dinitrogen pentoxide in the gas phase to give nitrogen dioxide and oxygen is a first order reaction. If the half life at 55 "C is 410 s, what is the value of the rate constant k? If the initial concentration of dinitrogen pentoxide in an expt at 55 °C was 0.200 M what will be the concentration of dinitrogen pentoxide, nitrogen dioxide and oxygen after 4 half-lives?

Explanation / Answer

For 1st order reaction:

ln[A]=kt+ln[A]o.

here [A] concentration at time = 56.0 m mol /L

[A0], initial concentration = 220.0 m mol /L

t = 1.22*10^4 s

thereore; rate constant k will be calculated as follows:

ln[A]=kt+ln[A]o.

ln 56.0 m mol /L =k * 1.22*104 s +ln 220.0 m mol /L

ln 56.0 m mol /L - ln 220.0 m mol /L =k * 1.22*10^4 s

- 1.368 m mol /L   =k * 1.22*10^4 s

k = 1.12 *10^-4 m mol /L / s

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