) The half life period of a first order reaction is 100 sec.Calculate the time requred for 80% completion.(2005)

) The half life period of a first order reaction is 100 sec.Calculate

1.	) The half life period of a first order reaction is 100 sec.Calculate the time requred for 80% completion.(2005)
Answer» The half life of a first order reaction is given by the equation,t(1/2) = 0.693/kWhere “k” is the rate constant.From the equation, we can calculate the rate constant.100= 0.693/kk = 0.693/100= 0.00693sec^(-1)Now, use the equationk= (2.303/t)log(initial conc./final conc.)After consuming 80% of the reactant, the final concentration will be 20% of the initial concentration.Assume, initial concentration is xFinal concentration is 20% of x = (20/100)x = 0.2xThereforeInitial conc./final conc. = x/0.2x = 5Substitute this in the above formula0.00693 = (2.303/t)log(5)0.00693= 2.303×0.698/tt = 231.96 secs.Therefore it takes 231.96 secs. to consume 80% of the reactant.