Question

If the half-life for decomposition of a drug is 9
hrs, how long will it take for 125mg of the drug
to decompose by 28%? Assume first-order
kinetics.

Answer 1

Answer:

4.2 hrs time required to complete 28% reaction

Answer 2

Answer:

Given: Half life (T

1/2

)=120 minutes

For 1st order reaction, Half life (T

1/2

)=

rateconstant(K)

0.693

Here, K=

120

0.693

=0.00578min

−1

Let initial concentration a mol and time t in minutes required for 90% decomposition of the compound

Now, t=

K

2.303

log

a−0.9a

a

=

0.00578

2.303

log10=398 minutes

Thus, 398 minutes are required for 90% decomposition of the compound.