Question

For a first order reaction
A B , the reaction rate
at reactant concentration of 0.01 M is found to be
2.0 x 10-5 mol L- s-! The half life period of the
reaction is
[AIPMT (Prelims)-2005]
(1) 220 s
(2) 30 s
(3) 300 s
(4) 347 s

Answer 1

347 seconds is the half life period.

Explanation:

The rate of a reaction is proportional to concentration of reactant to the power raised to its order.

$R =k.[A]$------(1)

Therefore, given the concentration of the reactant $[A]=0.01 M$

Rate is given R=2*10⁻⁵ MLS⁻¹

Therefore, substituting these in eqn (1)

we get $K=\frac{0.00002}{0.001} =0.002$

Half life period is given by $t(\frac{1}{2} )= \frac{0.693}{K}$

Therefore, $t(\frac{1}{2} )=\frac{0.693}{0.002} =346.5 s$

Therefore, the half life period is 347 s