In a study of the gas phase decomposition of hydrogen peroxide at 400 degree C H

Question

In a study of the gas phase decomposition of hydrogen peroxide at 400 degree C H_2O_2(g) rightarrow H_2O(g) + 1/2 O_2(g) the following data were obtained: The observed half life for this reaction when the starting concentration is 0.238 M is _________ s and when the starting concentration is 0.119 M is _________s. The average delta(I/[H_2O_2]) delta t from t = 0 s to t = 9.12 s is _______ M^-1 s^-1. The average delta(I/H_2O_2]. delta t from t = 9.12 s to t = 27.4 s is _________ M^-1 s^-1. Based on these data. the rate constant for this order reaction is _________ M^-1 s^-1.

Explanation / Answer

1) Step I

Half-life is the time when the concentration of the reactants have been reduced to 50%. From the table we can see that when initial concentration is 0.238M, half-life will be the time when the concentration will be (0.238/2) = 0.119M that is after 9.12sec.

Step II

Similarly, when the initial concentration is 0.119M, half-life will be the time when concentration becomes (0.119/2) = 0.0595M. From the table we can calculate that easily by converting 9.12sec to 0 sec then 27.4sec will become (27.4-9.12) = 18.28 sec that is the half-life.

2) Step I

1/[H2O2]t=0 = 4.201 M-1

Step II

1/[H2O2]t=9.12 = 8.403 M-1

Step III

Average = (8.403 - 4.201) / 9.12 = 0.461 M-1S-1

Similarly,

Step I

1/[H2O2]t=9.12 = 8.403 M-1

Step II

1/[H2O2]t=27.4 = 16.807 M-1

Step III

Average = (16.807 - 8.403) / (27.4 - 9.12) = 0.459 M-1S-1

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