Answer :
Answer : The time passed in years is [tex]1.49\times 10^4\text{ years}[/tex]
Explanation :
Half-life = 5000 years
First we have to calculate the rate constant, we use the formula :
[tex]k=\frac{0.693}{t_{1/2}}[/tex]
[tex]k=\frac{0.693}{5000\text{ years}}[/tex]
[tex]k=1.39\times 10^{-4}\text{ years}^{-1}[/tex]
Now we have to calculate the time passed.
Expression for rate law for first order kinetics is given by:
[tex]t=\frac{2.303}{k}\log\frac{a}{a-x}[/tex]
where,
k = rate constant = [tex]1.39\times 10^{-4}\text{ years}^{-1}[/tex]
t = time passed by the sample = ?
a = let initial amount of the reactant = X
a - x = amount left after decay process = [tex]\frac{X}{8}[/tex]
Now put all the given values in above equation, we get
[tex]t=\frac{2.303}{1.39\times 10^{-4}}\log\frac{X}{(\frac{X}{8})}[/tex]
[tex]t=14962.706\text{ years}=1.49\times 10^4\text{ years}[/tex]
Therefore, the time passed in years is [tex]1.49\times 10^4\text{ years}[/tex]
