Question

Half life period of first order reaction is 10 minutes.Starting with initial concentration 12m the rate after 20 min is

Answer 1

first find out rate constant then find out the concentration after 20 min and at last find the rate for that concentration

Answer 2

The concentration after 20 min is 3M

Explanation:

Expression for rate law for first order kinetics is given by:

$t=\frac{2.303}{k}\log\frac{a}{a-x}$

where,

k = rate constant

t = age of sample

a = let initial amount of the reactant

a - x = amount left after decay process  

Expression for rate law for first order kinetics is given by:

$Rate=k[A]^1$

a) for completion of half life:

Half life is the amount of time taken by a radioactive material to decay to half of its original value.

$t_{\frac{1}{2}}=\frac{0.693}{k}$

$k=\frac{0.693}{10min}=0.0693min^{-1}$

b)  for concentration after 20 min:

$t=\frac{2.303}{0.0693}\log\frac{12}{x}$

$20=\frac{2.303}{0.0693}\log\frac{100}{x}$

$x=3M$

The concentration after 20 min is 3M

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