Question

45
Half life of a first order reaction is 4 s and the
initial concentration of the reactants is 0.12 M
The concentration of the reactant left after 16 second
is
(a) 0.0075 M
(b) 0.06M
(c) 0,03M
(d) 0.015M​

Answer 1

The concentration of the reactant left after 16 second  is  0.0075 M

Explanation:

Formula used to calculate the concentration of the reactant left:

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

where,

a = amount of reactant left after n-half lives = ?

$a_o$ = Initial amount of the reactant = 0.12 M

n = number of half lives  = $\frac{text {total time}}{\text {half life}}=\frac{16s}{4s}=4$

Putting values in above equation, we get:

$a=\frac{0.12}{2^4}=\frac{0.12}{16}$

$a=0.0075M$

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