Question

Data for the decomposition of hydrogen peroxide at some set temperature T is include below. The rate law depends only on the concentration of H2O2. Answer questions 6, 7 and 8.
2 H2O2 ---> 2 H2O + O2
t (seconds)   0     ,   60    ,  120  ,   180 , 240 ,   360  ,   420 , 600
[H2O2] (M) 0.882, 0.697, 0.566 ,0.458, 0.372, 0.236, 0.188, 0.094

What is the value of the rate constant K?
What is the half life of the reaction when the initial concentration of H2O2 is 0.882 M?
What is the average rate of reaction, R, from t = 60 to t = 120?

Answer 1

(a)

2 H₂O₂   2 H₂O + O₂

Since the rate law depends only on the concentration of H2O2 and a first-order reaction has a rate proportional to the concentration of one reactant. So, its a first order reaction.

For first order reaction

k1 = (1/60 s) ln (0.882/0.697)

  k1 = (1/60) ln (1.265)

  k1 = 3.92 x 10^-3  s^-1

Half life of a first order reaction is given by

= (0.693) / (3.92 x 10^-3 s^-1 )

= 176 s

Average rate of reaction from t=60 to t= 120.

Here, t= 120-60 = 60 s

  

k1 = (1/60) ln (0.697/ 0.566)

= 3.47 x 10^-3 s^-1