Question

How many half lives are required to complete 93.75% of a first order reaction?​

Answer 1

Answer : The number of half lives required are, 4

Solution :

As we are given that,

The reaction completion = 93.75 %

That means,

Initial amount of the reactant = 100 g

Amount of reactant left = 100 - 93.75 = 6.25 g

Formula used :

$a=\frac{a_o}{2^n}\\\\2^n=\frac{a_o}{a}$

where,

$a_o$ = Initial amount of the reactant = 100 g

a = amount of reactant left after n-half lives = 6.25 g

n = number of half lives  = ?

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

$2^n=\frac{100g}{6.25g}$

$2^n=16$

$2^n=2^4$

$n=4$

Therefore, the number of half lives required are, 4