Question

If a substance with half life 3 days is taken at other place in 12days what amount of substance is lr

Answer 1

Hey mate here's your answer

If it has been 12 days, and the half life is 3 days, then it has been 4 half life cycles. This means you have one half of one half of one half of one half the amount that was there at the start of the 12 day period. 1/2 x 1/2 x 1/2×1/2 = 1/16, so 1/16 of initial amount.

Hope this helps you

Answer 2

The amount of substance after 12 days is $\frac{1}{16}$

Explanation:

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

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

$k=\frac{0.693}{3}=0.231days^{-1}$

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  = $0.231days^{-1}$

t = age of sample  = 12 days

a = let initial amount of the reactant  = 100

a - x = amount left after decay process = x

$12=\frac{2.303}{0.231}\log\frac{100}{x}$

$\log\frac{100}{x}=1.2$

$\frac{100}{x}=16$

$6.25=x$

$x=6.25$

$x=\frac{6.25}{100}=\frac{1}{16}$

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