The decomposition of hydrogen peroxide in dilute sodium hydroxide solution is de

Question

The decomposition of hydrogen peroxide in dilute sodium hydroxide solution is described by the equation:

2H2O2(aq) ----> 2H2O2(l) + O2(g).

The reaction is first order in H2O2, the rate constant for the comsumption of H2O2 at 20 degree C is 1.8 x 10-5s-1, and the initial concentration of  H2O2? is 0.30 M.

a) what is the concentration of  H2O2? after 4.00h?

b) How long will it take for the  H2O2? concentration to drop to 0.12 M?

c) How long will it take for 90% of the  H2O2? to decompose?

--If you dont mind explaining it I would really appreciate it! :) Thank you!

Explanation / Answer

a)   first order rate constant,

initial conc= a=0.30M ,

a-x = remaing concentration after time t

t= 4x3600sec

k = (2.303/t )( log a/a-x )

1.8x10-5= (2.303/4x3600)( log 0.3/a-x )

a-x = 0.23

concentration of  H2O2 after 4.00h= 0.23

b) k = (2.303/t )( log a/a-x )

1.8x10-5= (2.303/t)( log 0.3/0.12 )

t= 0.498 x105 sec

c) k = (2.303/t )( log a/a-x )

1.8x10-5 = (2.303/t )( log 100/10 )

t= 1.279x105 sec

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