Chemical Kinetics - Result Question 42
####42. 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 $16 s$ is
(a) $0.0075 M$
(b) $0.06 M$
(c) $0.03 M$
(d) $0.015 M$
[1999]
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Solution:
$ \begin{matrix} \text{ (a) } t _{1 / 2}=4 s & T=16 \\ n=\frac{T}{t _{1 / 2}}=\frac{16}{4}=4 \\ A=A_o(\frac{1}{2})^{n}=0.12 \times(\frac{1}{2})^{4}=\frac{0.12}{16}=0.0075 M \end{matrix} $
where $A_o=$ initial concentration &
$A=$ concentration left after time $t$.
