Question

A zero order reaction is 50% complete in 10 minutes. It is allowed to proceed for another 5 minutes. How much the reaction gets completed at the end of 15 minutes?

Answer 1

Answer : 75 % reaction will be completed at the end of 15 minutes.

Explanation :

First we have to calculate the rate constant.

As we are given that the 50 % reaction complete in 10 minutes that means,

$t_{1/2}=10min$

The relation between half-life and rate constant for zero order reaction is:

$t_{1/2}=\frac{[A_o]}{2k}$

Let the initial concentration be, 100 g

$10=\frac{100}{2k}$

$k=5min^{-1}$

Now we have to calculate the left amount.

Integrated rate law for zero order kinetics is given as:

$k=\frac{1}{t}([A_o]-[A])$

k = rate constant of the reaction  = $5min^{-1}$

$[A_o]$ = Concentration of reactant initially = 100 g

$[A]$ = Concentration of reactant at time t. = ?

t = time = 15 min

Now put all the given values in the above expression, we get:

$5=\frac{1}{15}(100-[A])$

$A=25g$

From this we conclude that the amount left after 15 minutes are 25 grams that means 75 % reaction will be completed at the end of 15 minutes.

Therefore, 75 % reaction will be completed at the end of 15 minutes.