Q13 of 50 Page 1

The thermal decomposition of HCO2 H is a first order reaction with a rate constant of 2.4 x 10-3 s-1 at a certain temperature. Calculate how long will it take for three- fourths of initial quantity of HCO2H to decompose. (log 0.25 = -0.6021).

We know, for first order kinetics,


k =


where, k = rate constant.


t = time taken.


a =initial concentration.


a-x = concentration left after t amount of time.


Now, k=2.4 x 10-3 s-1 as given in the question.


Now, we have to find out the time taken for the decomposition of three-fourths of the compound.


Decomposed part(x) = 0.75a


2.4 x 10-3=


∴ t =


= = 577.6sec. [If, log x = a, then log () = -a]


So, it will it take 577.6 sec for three- fourths of initial quantity of HCO2H to decompose.


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