Question

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

H₂O₂(g)H₂O(g) + ½ O₂(g)

the following data were obtained:

[H2O2], M	0.133	6.65×10-2	3.33×10-2	1.67×10-2
seconds	0	16.1	48.2	112

Hint: It is not necessary to graph these data.

(1)
The observed half life for this reaction when the starting concentration is 0.133 M is s and when the starting concentration is 6.65×10^-2 M is s.

(2)
The average (1/[H₂O₂]) / t from t = 0 s to t = 16.1 s is M^-1 s^-1.
The average (1/[H₂O₂]) / t from t = 16.1 s to t = 48.2 s is M^-1 s^-1.

(3)
Based on these data, the rate constant for this _______zerofirstsecond order reaction is M^-1 s^-1.

Answer 1

1.

Time required for the conversion of half of the initial concentration of reactants to products is called half life time.

From the given data,

(a)

Half life time when starting concentration is 0.133 M = 16.2 s

(b)

Half life time when the starting concentration is 6.65 x 10^-2 M = 48.2 s

2.

(a)

d[H2O2] / dt = - ( 6.65 x 10^-2 - 0.133 ) / 16.1 = 4.13 x 10^-3 M / s

(b)

d[H2O2] / dt = - ( 3.33 x 10^-2 - 6.65 x 10^-2 ) / ( 48.2 - 16.1 ) = 1.03 x 10^-3 M / s

3.

From (1)

Half life time increases with decrease in concentration of reactant.

Hence it is second order reaction.

For a second order reaction,

t1/2 = 1 / k[A]0

Half life time of second order reaction is inversely proportional to initial concentration of reactants,